diff --git a/filter/mathjaxloader/filter.php b/filter/mathjaxloader/filter.php
index 0906e18fb49..9fab93b9e79 100644
--- a/filter/mathjaxloader/filter.php
+++ b/filter/mathjaxloader/filter.php
@@ -140,7 +140,13 @@ class filter_mathjaxloader extends moodle_text_filter {
         if ($hasextra) {
             // If custom dilimeters are used, wrap whole text to prevent autolinking.
             $text = '<span class="nolink">' . $text . '</span>';
-        } else {
+        } else if (preg_match('/\\\\[[(]/', $text) || preg_match('/\$\$/', $text)) {
+            // Only parse the text if there are mathjax symbols in it. The recognized
+            // math environments are \[ \] and $$ $$ for display mathematics and \( \)
+            // for inline mathematics.
+            // Note: 2 separate regexes seems to perform better here than using a single
+            // regex with groupings.
+
             // Wrap display and inline math environments in nolink spans.
             // Do not wrap nested environments, i.e., if inline math is nested
             // inside display math, only the outer display math is wrapped in
diff --git a/lang/en/cache.php b/lang/en/cache.php
index 441b1910acf..73acbeb0803 100644
--- a/lang/en/cache.php
+++ b/lang/en/cache.php
@@ -65,6 +65,7 @@ $string['cachedef_observers'] = 'Event observers';
 $string['cachedef_plugin_functions'] = 'Plugins available callbacks';
 $string['cachedef_plugin_manager'] = 'Plugin info manager';
 $string['cachedef_presignup'] = 'Pre sign-up data for particular unregistered user';
+$string['cachedef_portfolio_add_button_portfolio_instances'] = 'Portfolio instances for portfolio_add_button class';
 $string['cachedef_postprocessedcss'] = 'Post processed CSS';
 $string['cachedef_tagindexbuilder'] = 'Search results for tagged items';
 $string['cachedef_questiondata'] = 'Question definitions';
diff --git a/lib/db/caches.php b/lib/db/caches.php
index 71ebe33add0..7247f54386a 100644
--- a/lib/db/caches.php
+++ b/lib/db/caches.php
@@ -391,4 +391,13 @@ $definitions = array(
         'simplekeys' => true,
         'simpledata' => true,
     ),
+
+    // Cache the list of portfolio instances for the logged in user
+    // in the portfolio_add_button constructor to avoid loading the
+    // same data multiple times.
+    'portfolio_add_button_portfolio_instances' => [
+        'mode' => cache_store::MODE_REQUEST,
+        'simplekeys' => true,
+        'staticacceleration' => true
+    ],
 );
diff --git a/lib/portfoliolib.php b/lib/portfoliolib.php
index 68d5fe500bf..cc00cc5b8a2 100644
--- a/lib/portfoliolib.php
+++ b/lib/portfoliolib.php
@@ -117,7 +117,14 @@ class portfolio_add_button {
             debugging('Building portfolio add button while portfolios is disabled. This code can be optimised.', DEBUG_DEVELOPER);
         }
 
-        $this->instances = portfolio_instances();
+        $cache = cache::make('core', 'portfolio_add_button_portfolio_instances');
+        $instances = $cache->get('instances');
+        if ($instances === false) {
+            $instances = portfolio_instances();
+            $cache->set('instances', $instances);
+        }
+
+        $this->instances = $instances;
         if (empty($options)) {
             return true;
         }
diff --git a/mod/forum/classes/local/builders/exported_discussion_summaries.php b/mod/forum/classes/local/builders/exported_discussion_summaries.php
index 7859c4796d1..bb792288268 100644
--- a/mod/forum/classes/local/builders/exported_discussion_summaries.php
+++ b/mod/forum/classes/local/builders/exported_discussion_summaries.php
@@ -105,7 +105,7 @@ class exported_discussion_summaries {
      *
      * @param stdClass $user The user to export the posts for.
      * @param forum_entity $forum The forum that each of the $discussions belong to
-     * @param discussion_entity[] $discussions A list of all discussions that each of the $posts belong to
+     * @param discussion_summary_entity[] $discussions A list of all discussion summaries to export
      * @return stdClass[] List of exported posts in the same order as the $posts array.
      */
     public function build(
@@ -125,6 +125,12 @@ class exported_discussion_summaries {
 
         $replycounts = $postvault->get_reply_count_for_discussion_ids($user, $discussionids, $canseeanyprivatereply);
         $latestposts = $postvault->get_latest_post_id_for_discussion_ids($user, $discussionids, $canseeanyprivatereply);
+        $postauthorids = array_unique(array_reduce($discussions, function($carry, $summary) {
+            $firstpostauthorid = $summary->get_first_post_author()->get_id();
+            $lastpostauthorid = $summary->get_latest_post_author()->get_id();
+            return array_merge($carry, [$firstpostauthorid, $lastpostauthorid]);
+        }, []));
+        $postauthorcontextids = $this->get_author_context_ids($postauthorids);
 
         $unreadcounts = [];
         $favourites = $this->get_favourites($user);
@@ -144,6 +150,7 @@ class exported_discussion_summaries {
             $replycounts,
             $unreadcounts,
             $latestposts,
+            $postauthorcontextids,
             $favourites
         );
 
@@ -224,4 +231,15 @@ class exported_discussion_summaries {
 
         return $authorgroups;
     }
+
+    /**
+     * Get the user context ids for each of the authors.
+     *
+     * @param int[] $authorids The list of author ids to fetch context ids for.
+     * @return int[] Context ids indexed by author id
+     */
+    private function get_author_context_ids(array $authorids) : array {
+        $authorvault = $this->vaultfactory->get_author_vault();
+        return $authorvault->get_context_ids_for_author_ids($authorids);
+    }
 }
diff --git a/mod/forum/classes/local/builders/exported_posts.php b/mod/forum/classes/local/builders/exported_posts.php
index 2d8934d971c..9e25386629b 100644
--- a/mod/forum/classes/local/builders/exported_posts.php
+++ b/mod/forum/classes/local/builders/exported_posts.php
@@ -137,6 +137,7 @@ class exported_posts {
         $groupedposts = $this->group_posts_by_discussion($forums, $discussions, $posts);
         // Load all of the resources we need in order to export the posts.
         $authorsbyid = $this->get_authors_for_posts($posts);
+        $authorcontextids = $this->get_author_context_ids(array_keys($authorsbyid));
         $attachmentsbypostid = $this->get_attachments_for_posts($groupedposts);
         $groupsbycourseandauthorid = $this->get_author_groups_from_posts($groupedposts);
         $tagsbypostid = $this->get_tags_from_posts($posts);
@@ -161,6 +162,7 @@ class exported_posts {
                 $discussion,
                 $groupedposts,
                 $authorsbyid,
+                $authorcontextids,
                 $attachmentsbypostid,
                 $groupsbycourseandauthorid[$courseid],
                 $readreceiptcollectionbyforumid[$forumid] ?? null,
@@ -248,6 +250,17 @@ class exported_posts {
         return $authorvault->get_authors_for_posts($posts);
     }
 
+    /**
+     * Get the user context ids for each of the authors.
+     *
+     * @param int[] $authorids The list of author ids to fetch context ids for.
+     * @return int[] Context ids indexed by author id
+     */
+    private function get_author_context_ids(array $authorids) : array {
+        $authorvault = $this->vaultfactory->get_author_vault();
+        return $authorvault->get_context_ids_for_author_ids($authorids);
+    }
+
     /**
      * Load the list of all attachments for the posts. The list of attachments will be
      * indexed by the post id.
diff --git a/mod/forum/classes/local/exporters/author.php b/mod/forum/classes/local/exporters/author.php
index fb648463e20..203fc82a350 100644
--- a/mod/forum/classes/local/exporters/author.php
+++ b/mod/forum/classes/local/exporters/author.php
@@ -42,6 +42,8 @@ require_once($CFG->dirroot . '/mod/forum/lib.php');
 class author extends exporter {
     /** @var author_entity $author Author entity */
     private $author;
+    /** @var int $authorcontextid The context id for the author entity */
+    private $authorcontextid;
     /** @var array $authorgroups List of groups that the author belongs to */
     private $authorgroups;
     /** @var bool $canview Should the author be anonymised? */
@@ -51,12 +53,20 @@ class author extends exporter {
      * Constructor.
      *
      * @param author_entity $author The author entity to export
+     * @param int $authorcontextid The context id for the author entity to export
      * @param stdClass[] $authorgroups The list of groups that the author belongs to
      * @param bool $canview Can the requesting user view this author or should it be anonymised?
      * @param array $related The related data for the export.
      */
-    public function __construct(author_entity $author, array $authorgroups = [], bool $canview = true, array $related = []) {
+    public function __construct(
+        author_entity $author,
+        int $authorcontextid,
+        array $authorgroups = [],
+        bool $canview = true,
+        array $related = []
+    ) {
         $this->author = $author;
+        $this->authorcontextid = $authorcontextid;
         $this->authorgroups = $authorgroups;
         $this->canview = $canview;
         return parent::__construct([], $related);
@@ -128,6 +138,7 @@ class author extends exporter {
      */
     protected function get_other_values(renderer_base $output) {
         $author = $this->author;
+        $authorcontextid = $this->authorcontextid;
         $urlfactory = $this->related['urlfactory'];
 
         if ($this->canview) {
@@ -148,7 +159,7 @@ class author extends exporter {
                 'groups' => $groups,
                 'urls' => [
                     'profile' => ($urlfactory->get_author_profile_url($author))->out(false),
-                    'profileimage' => ($urlfactory->get_author_profile_image_url($author))->out(false)
+                    'profileimage' => ($urlfactory->get_author_profile_image_url($author, $authorcontextid))->out(false)
                 ]
             ];
         } else {
diff --git a/mod/forum/classes/local/exporters/discussion_summaries.php b/mod/forum/classes/local/exporters/discussion_summaries.php
index 13eac7e8527..e5fbb36820a 100644
--- a/mod/forum/classes/local/exporters/discussion_summaries.php
+++ b/mod/forum/classes/local/exporters/discussion_summaries.php
@@ -56,6 +56,9 @@ class discussion_summaries extends exporter {
     /** @var array The latest post in each discussion */
     private $latestpostids;
 
+    /** @var int[] The context ids for the first and latest post authors (indexed by author id) */
+    private $postauthorcontextids;
+
     /**
      * Constructor.
      *
@@ -65,6 +68,7 @@ class discussion_summaries extends exporter {
      * @param int[] $discussionreplycount Discussion reply counts indexed by dicussion id
      * @param int[] $discussionunreadcount Discussion unread counts indexed by dicussion id
      * @param int[] $latestpostids List of latest post ids indexed by discussion id
+     * @param int[] $postauthorcontextids The context ids for the first and latest post authors (indexed by author id)
      * @param array $related The related
      */
     public function __construct(
@@ -74,6 +78,7 @@ class discussion_summaries extends exporter {
         array $discussionreplycount,
         array $discussionunreadcount,
         array $latestpostids,
+        array $postauthorcontextids,
         array $related = []
     ) {
         $this->discussions = $discussions;
@@ -82,6 +87,7 @@ class discussion_summaries extends exporter {
         $this->discussionreplycount = $discussionreplycount;
         $this->discussionunreadcount = $discussionunreadcount;
         $this->latestpostids = $latestpostids;
+        $this->postauthorcontextids = $postauthorcontextids;
         return parent::__construct([], $related);
     }
 
@@ -126,6 +132,8 @@ class discussion_summaries extends exporter {
                     $replycount,
                     $unreadcount,
                     $latestpostid,
+                    $this->postauthorcontextids[$discussion->get_first_post_author()->get_id()],
+                    $this->postauthorcontextids[$discussion->get_latest_post_author()->get_id()],
                     $related
                 );
             $exporteddiscussions[] = $exporter->export($output);
diff --git a/mod/forum/classes/local/exporters/discussion_summary.php b/mod/forum/classes/local/exporters/discussion_summary.php
index 6ba2bcb531c..3d009ee222d 100644
--- a/mod/forum/classes/local/exporters/discussion_summary.php
+++ b/mod/forum/classes/local/exporters/discussion_summary.php
@@ -55,6 +55,12 @@ class discussion_summary extends exporter {
     /** @var int The latest post id in the discussion */
     private $latestpostid;
 
+    /** @var int The context id for the author of the first post */
+    private $firstpostauthorcontextid;
+
+    /** @var int The context id for the author of the latest post */
+    private $latestpostauthorcontextid;
+
     /**
      * Constructor.
      *
@@ -64,6 +70,8 @@ class discussion_summary extends exporter {
      * @param int $replycount The number of replies to the discussion
      * @param int $unreadcount number of unread posts if the user is tracking these
      * @param int $latestpostid The latest post id in the discussion
+     * @param int $firstpostauthorcontextid The context id for the author of the first post
+     * @param int $latestpostauthorcontextid The context id for the author of the latest post
      * @param array $related The related objects
      */
     public function __construct(
@@ -73,6 +81,8 @@ class discussion_summary extends exporter {
         int $replycount,
         int $unreadcount,
         int $latestpostid,
+        int $firstpostauthorcontextid,
+        int $latestpostauthorcontextid,
         array $related = []
     ) {
         $this->summary = $summary;
@@ -81,6 +91,8 @@ class discussion_summary extends exporter {
         $this->replycount = $replycount;
         $this->unreadcount = $unreadcount;
         $this->latestpostid = $latestpostid;
+        $this->firstpostauthorcontextid = $firstpostauthorcontextid;
+        $this->latestpostauthorcontextid = $latestpostauthorcontextid;
         return parent::__construct([], $related);
     }
 
@@ -131,6 +143,7 @@ class discussion_summary extends exporter {
 
         $firstpostauthor = new author(
             $this->summary->get_first_post_author(),
+            $this->firstpostauthorcontextid,
             $this->groupsbyauthorid[$this->summary->get_first_post_author()->get_id()],
             $capabilitymanager->can_view_post(
                 $user,
@@ -142,6 +155,7 @@ class discussion_summary extends exporter {
 
         $latestpostauthor = new author(
             $this->summary->get_latest_post_author(),
+            $this->latestpostauthorcontextid,
             [],
             $capabilitymanager->can_view_post(
                 $user,
diff --git a/mod/forum/classes/local/exporters/post.php b/mod/forum/classes/local/exporters/post.php
index 00716d6a940..ea097b4aa8c 100644
--- a/mod/forum/classes/local/exporters/post.php
+++ b/mod/forum/classes/local/exporters/post.php
@@ -333,6 +333,7 @@ class post extends exporter {
         $forum = $this->related['forum'];
         $discussion = $this->related['discussion'];
         $author = $this->related['author'];
+        $authorcontextid = $this->related['authorcontextid'];
         $user = $this->related['user'];
         $readreceiptcollection = $this->related['readreceiptcollection'];
         $rating = $this->related['rating'];
@@ -368,7 +369,13 @@ class post extends exporter {
         $markasunreadurl = $cancontrolreadstatus ? $urlfactory->get_mark_post_as_unread_url_from_post($post) : null;
         $discussurl = $canview ? $urlfactory->get_discussion_view_url_from_post($post) : null;
 
-        $authorexporter = new author_exporter($author, $authorgroups, ($canview && !$isdeleted), $this->related);
+        $authorexporter = new author_exporter(
+            $author,
+            $authorcontextid,
+            $authorgroups,
+            ($canview && !$isdeleted),
+            $this->related
+        );
         $exportedauthor = $authorexporter->export($output);
         // Only bother loading the content if the user can see it.
         $loadcontent = $canview && !$isdeleted;
@@ -448,6 +455,7 @@ class post extends exporter {
             'forum' => 'mod_forum\local\entities\forum',
             'discussion' => 'mod_forum\local\entities\discussion',
             'author' => 'mod_forum\local\entities\author',
+            'authorcontextid' => 'int?',
             'user' => 'stdClass',
             'context' => 'context',
             'authorgroups' => 'stdClass[]',
diff --git a/mod/forum/classes/local/exporters/posts.php b/mod/forum/classes/local/exporters/posts.php
index f00e3fc82a3..1ba0a76dad5 100644
--- a/mod/forum/classes/local/exporters/posts.php
+++ b/mod/forum/classes/local/exporters/posts.php
@@ -45,6 +45,8 @@ class posts extends exporter {
     private $posts;
     /** @var author_entity[] $authorsbyid List of authors for the posts indexed by author id */
     private $authorsbyid;
+    /** @var int[] $authorcontextids List of authors context ids indexed by author id */
+    private $authorcontextids;
     /** @var array $attachmentsbypostid List of attachments indexed by post id */
     private $attachmentsbypostid;
     /** @var array $groupsbyauthorid List of author's groups indexed by author id */
@@ -59,6 +61,7 @@ class posts extends exporter {
      *
      * @param post_entity[] $posts List of posts to export
      * @param author_entity[] $authorsbyid List of authors for the posts indexed by author id
+     * @param int[] $authorcontextids List of authors context ids indexed by author id
      * @param array $attachmentsbypostid List of attachments indexed by post id
      * @param array $groupsbyauthorid List of author's groups indexed by author id
      * @param array $tagsbypostid List of tags indexed by post id
@@ -68,6 +71,7 @@ class posts extends exporter {
     public function __construct(
         array $posts,
         array $authorsbyid = [],
+        array $authorcontextids = [],
         array $attachmentsbypostid = [],
         array $groupsbyauthorid = [],
         array $tagsbypostid = [],
@@ -76,6 +80,7 @@ class posts extends exporter {
     ) {
         $this->posts = $posts;
         $this->authorsbyid = $authorsbyid;
+        $this->authorcontextids = $authorcontextids;
         $this->attachmentsbypostid = $attachmentsbypostid;
         $this->groupsbyauthorid = $groupsbyauthorid;
         $this->tagsbypostid = $tagsbypostid;
@@ -106,6 +111,7 @@ class posts extends exporter {
     protected function get_other_values(renderer_base $output) {
         $related = $this->related;
         $authorsbyid = $this->authorsbyid;
+        $authorcontextids = $this->authorcontextids;
         $attachmentsbypostid = $this->attachmentsbypostid;
         $groupsbyauthorid = $this->groupsbyauthorid;
         $tagsbypostid = $this->tagsbypostid;
@@ -114,6 +120,7 @@ class posts extends exporter {
             function($post) use (
                 $related,
                 $authorsbyid,
+                $authorcontextids,
                 $attachmentsbypostid,
                 $groupsbyauthorid,
                 $tagsbypostid,
@@ -123,12 +130,14 @@ class posts extends exporter {
                 $authorid = $post->get_author_id();
                 $postid = $post->get_id();
                 $author = isset($authorsbyid[$authorid]) ? $authorsbyid[$authorid] : [];
+                $authorcontextid = isset($authorcontextids[$authorid]) ? $authorcontextids[$authorid] : null;
                 $attachments = isset($attachmentsbypostid[$postid]) ? $attachmentsbypostid[$postid] : [];
                 $authorgroups = isset($groupsbyauthorid[$authorid]) ? $groupsbyauthorid[$authorid] : [];
                 $tags = isset($tagsbypostid[$postid]) ? $tagsbypostid[$postid] : [];
                 $rating = isset($ratingbypostid[$postid]) ? $ratingbypostid[$postid] : null;
                 $exporter = new post_exporter($post, array_merge($related, [
                     'author' => $author,
+                    'authorcontextid' => $authorcontextid,
                     'attachments' => $attachments,
                     'authorgroups' => $authorgroups,
                     'tags' => $tags,
diff --git a/mod/forum/classes/local/factories/exporter.php b/mod/forum/classes/local/factories/exporter.php
index 8aaea94e265..e7c405a9dda 100644
--- a/mod/forum/classes/local/factories/exporter.php
+++ b/mod/forum/classes/local/factories/exporter.php
@@ -152,12 +152,14 @@ class exporter {
      *
      * @param   stdClass        $user The user viewing the forum
      * @param   forum_entity    $forum The forum being viewed
-     * @param   discussion_entity[] $discussions The set of discussions to be shown
+     * @param   discussion_summary_entity[] $discussions The set of discussion summaries to export
      * @param   stdClass[]      $groupsbyauthorid The set of groups in an associative array for each author
      * @param   stdClass[]      $groupsbyid The set of groups in the forum in an associative array for each group
      * @param   int[]           $discussionreplycount The number of replies for each discussion
      * @param   int[]           $discussionunreadcount The number of unread posts for each discussion
      * @param   int[]           $latestpostids The latest post id for each discussion
+     * @param   int[]           $postauthorcontextids The context ids for the first and last post authors (indexed by author id)
+     * @param   int[]           $favourites The list of discussion ids that have been favourited
      * @return  discussion_summaries_exporter
      */
     public function get_discussion_summaries_exporter(
@@ -168,7 +170,8 @@ class exporter {
         array $groupsbyauthorid = [],
         array $discussionreplycount = [],
         array $discussionunreadcount = [],
-        array $latestpostid = [],
+        array $latestpostids = [],
+        array $postauthorcontextids = [],
         array $favourites = []
     ) : discussion_summaries_exporter {
         return new discussion_summaries_exporter(
@@ -177,7 +180,8 @@ class exporter {
             $groupsbyauthorid,
             $discussionreplycount,
             $discussionunreadcount,
-            $latestpostid,
+            $latestpostids,
+            $postauthorcontextids,
             [
                 'legacydatamapperfactory' => $this->legacydatamapperfactory,
                 'context' => $forum->get_context(),
@@ -207,6 +211,7 @@ class exporter {
      * @param   discussion_entity $discussion The discussion that the post is in
      * @param   post_entity[]   $posts The set of posts to be exported
      * @param   author_entity[] $authorsbyid List of authors indexed by author id
+     * @param   int[]           $authorcontextids List of authors context ids indexed by author id
      * @param   array           $attachmentsbypostid List of attachments for each post indexed by post id
      * @param   array           $groupsbyauthorid List of groups for the post authors indexed by author id
      * @param   post_read_receipt_collection_entity|null $readreceiptcollection Details of read receipts for each post
@@ -221,6 +226,7 @@ class exporter {
         discussion_entity $discussion,
         array $posts,
         array $authorsbyid = [],
+        array $authorcontextids = [],
         array $attachmentsbypostid = [],
         array $groupsbyauthorid = [],
         post_read_receipt_collection_entity $readreceiptcollection = null,
@@ -228,16 +234,25 @@ class exporter {
         array $ratingbypostid = [],
         bool $includehtml = false
     ) : posts_exporter {
-        return new posts_exporter($posts, $authorsbyid, $attachmentsbypostid, $groupsbyauthorid, $tagsbypostid, $ratingbypostid, [
-            'capabilitymanager' => $this->managerfactory->get_capability_manager($forum),
-            'urlfactory' => $this->urlfactory,
-            'forum' => $forum,
-            'discussion' => $discussion,
-            'user' => $user,
-            'context' => $forum->get_context(),
-            'readreceiptcollection' => $readreceiptcollection,
-            'includehtml' => $includehtml
-        ]);
+        return new posts_exporter(
+            $posts,
+            $authorsbyid,
+            $authorcontextids,
+            $attachmentsbypostid,
+            $groupsbyauthorid,
+            $tagsbypostid,
+            $ratingbypostid,
+            [
+                'capabilitymanager' => $this->managerfactory->get_capability_manager($forum),
+                'urlfactory' => $this->urlfactory,
+                'forum' => $forum,
+                'discussion' => $discussion,
+                'user' => $user,
+                'context' => $forum->get_context(),
+                'readreceiptcollection' => $readreceiptcollection,
+                'includehtml' => $includehtml
+            ]
+        );
     }
 
     /**
diff --git a/mod/forum/classes/local/factories/url.php b/mod/forum/classes/local/factories/url.php
index 2d9f7a7586e..eaab4f59cbe 100644
--- a/mod/forum/classes/local/factories/url.php
+++ b/mod/forum/classes/local/factories/url.php
@@ -393,16 +393,19 @@ class url {
     }
 
     /**
-     * Get the url to view the author's profile image.
+     * Get the url to view the author's profile image. The author's context id should be
+     * provided to prevent the code from needing to load it.
      *
      * @param author_entity $author The author
+     * @param int|null $authorcontextid The author context id
      * @return moodle_url
      */
-    public function get_author_profile_image_url(author_entity $author) : moodle_url {
+    public function get_author_profile_image_url(author_entity $author, int $authorcontextid = null) : moodle_url {
         global $PAGE;
 
         $datamapper = $this->legacydatamapperfactory->get_author_data_mapper();
         $record = $datamapper->to_legacy_object($author);
+        $record->contextid = $authorcontextid;
         $userpicture = new user_picture($record);
         $userpicture->size = 2;
 
diff --git a/mod/forum/classes/local/renderers/discussion.php b/mod/forum/classes/local/renderers/discussion.php
index 8b7e6249186..084122a7af7 100644
--- a/mod/forum/classes/local/renderers/discussion.php
+++ b/mod/forum/classes/local/renderers/discussion.php
@@ -284,7 +284,7 @@ class discussion {
      *
      * @return string
      */
-    private function get_move_discussion_html() : string {
+    private function get_move_discussion_html() : ?string {
         global $DB;
 
         $forum = $this->forum;
diff --git a/mod/forum/classes/local/vaults/author.php b/mod/forum/classes/local/vaults/author.php
index bd0f78b90a0..730f0e1b9f0 100644
--- a/mod/forum/classes/local/vaults/author.php
+++ b/mod/forum/classes/local/vaults/author.php
@@ -99,4 +99,22 @@ class author extends db_table_vault {
         $authorids = array_keys($authorids);
         return $this->get_from_ids($authorids);
     }
+
+    /**
+     * Get the context ids for a set of author ids. The results are indexed
+     * by the author id.
+     *
+     * @param int[] $authorids The list of author ids to fetch.
+     * @return int[] Results indexed by author id.
+     */
+    public function get_context_ids_for_author_ids(array $authorids) : array {
+        $db = $this->get_db();
+        [$insql, $params] = $db->get_in_or_equal($authorids);
+        $sql = "SELECT instanceid, id FROM {context} WHERE contextlevel = ? AND instanceid {$insql}";
+        $records = $db->get_records_sql($sql, array_merge([CONTEXT_USER], $params));
+        return array_reduce($authorids, function($carry, $id) use ($records) {
+            $carry[$id] = isset($records[$id]) ? (int) $records[$id]->id : null;
+            return $carry;
+        }, []);
+    }
 }
diff --git a/mod/forum/tests/exporters_author_test.php b/mod/forum/tests/exporters_author_test.php
index 5dc0baa383b..9942e7f26e1 100644
--- a/mod/forum/tests/exporters_author_test.php
+++ b/mod/forum/tests/exporters_author_test.php
@@ -60,7 +60,7 @@ class mod_forum_exporters_author_testcase extends advanced_testcase {
             'test@example.com'
         );
 
-        $exporter = new author_exporter($author, [], true, [
+        $exporter = new author_exporter($author, 1, [], true, [
             'urlfactory' => \mod_forum\local\container::get_url_factory(),
             'context' => $context
         ]);
@@ -100,7 +100,7 @@ class mod_forum_exporters_author_testcase extends advanced_testcase {
 
         $group = $datagenerator->create_group(['courseid' => $course->id]);
 
-        $exporter = new author_exporter($author, [$group], true, [
+        $exporter = new author_exporter($author, 1, [$group], true, [
             'urlfactory' => \mod_forum\local\container::get_url_factory(),
             'context' => $context
         ]);
@@ -137,7 +137,7 @@ class mod_forum_exporters_author_testcase extends advanced_testcase {
 
         $group = $datagenerator->create_group(['courseid' => $course->id]);
 
-        $exporter = new author_exporter($author, [$group], false, [
+        $exporter = new author_exporter($author, 1, [$group], false, [
             'urlfactory' => \mod_forum\local\container::get_url_factory(),
             'context' => $context
         ]);
diff --git a/mod/forum/tests/exporters_post_test.php b/mod/forum/tests/exporters_post_test.php
index 561b0002808..daf675a3b5e 100644
--- a/mod/forum/tests/exporters_post_test.php
+++ b/mod/forum/tests/exporters_post_test.php
@@ -118,6 +118,7 @@ class mod_forum_exporters_post_testcase extends advanced_testcase {
         $discussion = $entityfactory->get_discussion_from_stdclass($discussion);
         $post = $entityfactory->get_post_from_stdclass($post);
         $author = $entityfactory->get_author_from_stdclass($user);
+        $authorcontext = context_user::instance($author->get_id());
 
         $exporter = new post_exporter($post, [
             'legacydatamapperfactory' => \mod_forum\local\container::get_legacy_data_mapper_factory(),
@@ -127,6 +128,7 @@ class mod_forum_exporters_post_testcase extends advanced_testcase {
             'forum' => $forum,
             'discussion' => $discussion,
             'author' => $author,
+            'authorcontextid' => $authorcontext->id,
             'user' => $user,
             'context' => $context,
             'authorgroups' => [],
@@ -246,6 +248,7 @@ class mod_forum_exporters_post_testcase extends advanced_testcase {
         $discussion = $entityfactory->get_discussion_from_stdclass($discussion);
         $post = $entityfactory->get_post_from_stdclass($post);
         $author = $entityfactory->get_author_from_stdclass($user);
+        $authorcontext = context_user::instance($author->get_id());
 
         $exporter = new post_exporter($post, [
             'legacydatamapperfactory' => \mod_forum\local\container::get_legacy_data_mapper_factory(),
@@ -255,6 +258,7 @@ class mod_forum_exporters_post_testcase extends advanced_testcase {
             'forum' => $forum,
             'discussion' => $discussion,
             'author' => $author,
+            'authorcontextid' => $authorcontext->id,
             'user' => $user,
             'context' => $context,
             'authorgroups' => [],
@@ -352,6 +356,7 @@ class mod_forum_exporters_post_testcase extends advanced_testcase {
         $discussion = $entityfactory->get_discussion_from_stdclass($discussion);
         $post = $entityfactory->get_post_from_stdclass($post);
         $author = $entityfactory->get_author_from_stdclass($user);
+        $authorcontext = context_user::instance($author->get_id());
 
         $exporter = new post_exporter($post, [
             'legacydatamapperfactory' => \mod_forum\local\container::get_legacy_data_mapper_factory(),
@@ -361,6 +366,7 @@ class mod_forum_exporters_post_testcase extends advanced_testcase {
             'forum' => $forum,
             'discussion' => $discussion,
             'author' => $author,
+            'authorcontextid' => $authorcontext->id,
             'user' => $user,
             'context' => $context,
             'authorgroups' => [],
diff --git a/mod/forum/tests/vaults_author_test.php b/mod/forum/tests/vaults_author_test.php
index 86d8b21a219..b35d0ea59c4 100644
--- a/mod/forum/tests/vaults_author_test.php
+++ b/mod/forum/tests/vaults_author_test.php
@@ -46,4 +46,38 @@ class mod_forum_vaults_author_testcase extends advanced_testcase {
 
         $this->assertEquals($user->id, $author->get_id());
     }
+
+    /**
+     * Test get_context_ids_for_author_ids.
+     */
+    public function test_get_context_ids_for_author_ids() {
+        $this->resetAfterTest();
+
+        $user1 = $this->getDataGenerator()->create_user();
+        $user2 = $this->getDataGenerator()->create_user();
+        $user3 = $this->getDataGenerator()->create_user();
+        $userid1 = $user1->id;
+        $userid2 = $user2->id;
+        $userid3 = $user3->id;
+        $fakeuserid = $user3->id + 1000;
+        $vaultfactory = \mod_forum\local\container::get_vault_factory();
+        $authorvault = $vaultfactory->get_author_vault();
+        $user1context = context_user::instance($user1->id);
+        $user2context = context_user::instance($user2->id);
+        $user3context = context_user::instance($user3->id);
+        $user1contextid = $user1context->id;
+        $user2contextid = $user2context->id;
+        $user3contextid = $user3context->id;
+        $fakeusercontextid = null;
+        $userids = [$userid1, $userid2, $userid3, $fakeuserid];
+
+        $expected = [
+            $userid1 => $user1contextid,
+            $userid2 => $user2contextid,
+            $userid3 => $user3contextid,
+            $fakeuserid => $fakeusercontextid
+        ];
+
+        $this->assertEquals($expected, $authorvault->get_context_ids_for_author_ids($userids));
+    }
 }