diff --git a/calendar/classes/local/event/strategies/raw_event_retrieval_strategy.php b/calendar/classes/local/event/strategies/raw_event_retrieval_strategy.php
index 7d1836149e0..252d37412fe 100644
--- a/calendar/classes/local/event/strategies/raw_event_retrieval_strategy.php
+++ b/calendar/classes/local/event/strategies/raw_event_retrieval_strategy.php
@@ -228,7 +228,7 @@ class raw_event_retrieval_strategy implements raw_event_retrieval_strategy_inter
         $subquery = "SELECT ev.modulename,
                             ev.instance,
                             ev.eventtype,
-                            MAX(ev.priority) as priority
+                            MIN(ev.priority) as priority
                        FROM {event} ev
                       $subquerywhere
                    GROUP BY ev.modulename, ev.instance, ev.eventtype";
diff --git a/calendar/lib.php b/calendar/lib.php
index 94233f1c41d..5df2607af51 100644
--- a/calendar/lib.php
+++ b/calendar/lib.php
@@ -123,7 +123,7 @@ define('CALENDAR_SUBSCRIPTION_REMOVE', 2);
 /**
  * CALENDAR_EVENT_USER_OVERRIDE_PRIORITY - Constant for the user override priority.
  */
-define('CALENDAR_EVENT_USER_OVERRIDE_PRIORITY', 9999999);
+define('CALENDAR_EVENT_USER_OVERRIDE_PRIORITY', 0);
 
 /**
  * CALENDAR_EVENT_TYPE_STANDARD - Standard events.
@@ -1233,7 +1233,7 @@ function calendar_get_events($tstart, $tend, $users, $groups, $courses, $withdur
     $subquery = "SELECT ev.modulename,
                             ev.instance,
                             ev.eventtype,
-                            MAX(ev.priority) as priority
+                            MIN(ev.priority) as priority
                        FROM {event} ev
                       $subquerywhere
                    GROUP BY ev.modulename, ev.instance, ev.eventtype";
diff --git a/calendar/tests/lib_test.php b/calendar/tests/lib_test.php
index 750bb9012d8..837692e7c73 100644
--- a/calendar/tests/lib_test.php
+++ b/calendar/tests/lib_test.php
@@ -223,7 +223,7 @@ class core_calendar_lib_testcase extends advanced_testcase {
         $events = calendar_get_events($timestart, $timeend, $group12student->id, $groups, $course->id);
         $this->assertCount(1, $events);
         $event = reset($events);
-        $this->assertEquals('Assignment 1 due date - Group B override', $event->name);
+        $this->assertEquals('Assignment 1 due date - Group A override', $event->name);
         // Get events for user that belongs to group A and has no user override events.
         $this->setUser($group1student);
         $events = calendar_get_events($timestart, $timeend, $group1student->id, $groups, $course->id);
@@ -524,7 +524,7 @@ class core_calendar_lib_testcase extends advanced_testcase {
         $events = calendar_get_legacy_events($timestart, $timeend, $group12student->id, $groups, $course->id);
         $this->assertCount(1, $events);
         $event = reset($events);
-        $this->assertEquals('Assignment 1 due date - Group B override', $event->name);
+        $this->assertEquals('Assignment 1 due date - Group A override', $event->name);
 
         // Get events for user that belongs to group A and has no user override events.
         $this->setUser($group1student);
diff --git a/calendar/tests/local_api_test.php b/calendar/tests/local_api_test.php
index b206454f12d..5e4b16a05c7 100644
--- a/calendar/tests/local_api_test.php
+++ b/calendar/tests/local_api_test.php
@@ -675,4 +675,187 @@ class core_calendar_local_api_testcase extends advanced_testcase {
         $event = reset($events);
         $this->assertEquals('assign', $event->modulename);
     }
+
+    /**
+     * Test for \core_calendar\local\api::get_legacy_events() when there are user and group overrides.
+     */
+    public function test_get_legacy_events_with_overrides() {
+        $generator = $this->getDataGenerator();
+
+        $course = $generator->create_course();
+
+        $plugingenerator = $this->getDataGenerator()->get_plugin_generator('mod_assign');
+        if (!isset($params['course'])) {
+            $params['course'] = $course->id;
+        }
+
+        $instance = $plugingenerator->create_instance($params);
+
+        // Create users.
+        $useroverridestudent = $generator->create_user();
+        $group1student = $generator->create_user();
+        $group2student = $generator->create_user();
+        $group12student = $generator->create_user();
+        $nogroupstudent = $generator->create_user();
+
+        // Enrol users.
+        $generator->enrol_user($useroverridestudent->id, $course->id, 'student');
+        $generator->enrol_user($group1student->id, $course->id, 'student');
+        $generator->enrol_user($group2student->id, $course->id, 'student');
+        $generator->enrol_user($group12student->id, $course->id, 'student');
+        $generator->enrol_user($nogroupstudent->id, $course->id, 'student');
+
+        // Create groups.
+        $group1 = $generator->create_group(['courseid' => $course->id]);
+        $group2 = $generator->create_group(['courseid' => $course->id]);
+
+        // Add members to groups.
+        $generator->create_group_member(['groupid' => $group1->id, 'userid' => $group1student->id]);
+        $generator->create_group_member(['groupid' => $group2->id, 'userid' => $group2student->id]);
+        $generator->create_group_member(['groupid' => $group1->id, 'userid' => $group12student->id]);
+        $generator->create_group_member(['groupid' => $group2->id, 'userid' => $group12student->id]);
+        $now = time();
+
+        // Events with the same module name, instance and event type.
+        $events = [
+            [
+                'name' => 'Assignment 1 due date',
+                'description' => '',
+                'format' => 0,
+                'courseid' => $course->id,
+                'groupid' => 0,
+                'userid' => 2,
+                'modulename' => 'assign',
+                'instance' => $instance->id,
+                'eventtype' => 'due',
+                'timestart' => $now,
+                'timeduration' => 0,
+                'visible' => 1
+            ], [
+                'name' => 'Assignment 1 due date - User override',
+                'description' => '',
+                'format' => 1,
+                'courseid' => 0,
+                'groupid' => 0,
+                'userid' => $useroverridestudent->id,
+                'modulename' => 'assign',
+                'instance' => $instance->id,
+                'eventtype' => 'due',
+                'timestart' => $now + 86400,
+                'timeduration' => 0,
+                'visible' => 1,
+                'priority' => CALENDAR_EVENT_USER_OVERRIDE_PRIORITY
+            ], [
+                'name' => 'Assignment 1 due date - Group A override',
+                'description' => '',
+                'format' => 1,
+                'courseid' => $course->id,
+                'groupid' => $group1->id,
+                'userid' => 2,
+                'modulename' => 'assign',
+                'instance' => $instance->id,
+                'eventtype' => 'due',
+                'timestart' => $now + (2 * 86400),
+                'timeduration' => 0,
+                'visible' => 1,
+                'priority' => 1,
+            ], [
+                'name' => 'Assignment 1 due date - Group B override',
+                'description' => '',
+                'format' => 1,
+                'courseid' => $course->id,
+                'groupid' => $group2->id,
+                'userid' => 2,
+                'modulename' => 'assign',
+                'instance' => $instance->id,
+                'eventtype' => 'due',
+                'timestart' => $now + (3 * 86400),
+                'timeduration' => 0,
+                'visible' => 1,
+                'priority' => 2,
+            ],
+        ];
+
+        foreach ($events as $event) {
+            calendar_event::create($event, false);
+        }
+
+        $timestart = $now - 100;
+        $timeend = $now + (3 * 86400);
+        $groups = [$group1->id, $group2->id];
+
+        // Get user override events.
+        $this->setUser($useroverridestudent);
+        $events = calendar_get_legacy_events($timestart, $timeend, $useroverridestudent->id, $groups, $course->id);
+        $this->assertCount(1, $events);
+        $event = reset($events);
+        $this->assertEquals('Assignment 1 due date - User override', $event->name);
+
+        // Get event for user with override but with the timestart and timeend parameters only covering the original event.
+        $events = calendar_get_legacy_events($timestart, $now, $useroverridestudent->id, $groups, $course->id);
+        $this->assertCount(0, $events);
+
+        // Get events for user that does not belong to any group and has no user override events.
+        $this->setUser($nogroupstudent);
+        $events = calendar_get_legacy_events($timestart, $timeend, $nogroupstudent->id, $groups, $course->id);
+        $this->assertCount(1, $events);
+        $event = reset($events);
+        $this->assertEquals('Assignment 1 due date', $event->name);
+
+        // Get events for user that belongs to groups A and B and has no user override events.
+        $this->setUser($group12student);
+        $events = calendar_get_legacy_events($timestart, $timeend, $group12student->id, $groups, $course->id);
+        $this->assertCount(1, $events);
+        $event = reset($events);
+        $this->assertEquals('Assignment 1 due date - Group A override', $event->name);
+
+        // Get events for user that belongs to group A and has no user override events.
+        $this->setUser($group1student);
+        $events = calendar_get_legacy_events($timestart, $timeend, $group1student->id, $groups, $course->id);
+        $this->assertCount(1, $events);
+        $event = reset($events);
+        $this->assertEquals('Assignment 1 due date - Group A override', $event->name);
+
+        // Add repeating events.
+        $repeatingevents = [
+            [
+                'name' => 'Repeating site event',
+                'description' => '',
+                'format' => 1,
+                'courseid' => SITEID,
+                'groupid' => 0,
+                'userid' => 2,
+                'repeatid' => $event->id,
+                'modulename' => '0',
+                'instance' => 0,
+                'eventtype' => 'site',
+                'timestart' => $now + 86400,
+                'timeduration' => 0,
+                'visible' => 1,
+            ],
+            [
+                'name' => 'Repeating site event',
+                'description' => '',
+                'format' => 1,
+                'courseid' => SITEID,
+                'groupid' => 0,
+                'userid' => 2,
+                'repeatid' => $event->id,
+                'modulename' => '0',
+                'instance' => 0,
+                'eventtype' => 'site',
+                'timestart' => $now + (2 * 86400),
+                'timeduration' => 0,
+                'visible' => 1,
+            ],
+        ];
+
+        foreach ($repeatingevents as $event) {
+            calendar_event::create($event, false);
+        }
+
+        // Make sure repeating events are not filtered out.
+        $events = calendar_get_legacy_events($timestart, $timeend, true, true, true);
+        $this->assertCount(3, $events);
+    }
 }
diff --git a/calendar/tests/raw_event_retrieval_strategy_test.php b/calendar/tests/raw_event_retrieval_strategy_test.php
index cbf8d706d40..82d77948ad9 100644
--- a/calendar/tests/raw_event_retrieval_strategy_test.php
+++ b/calendar/tests/raw_event_retrieval_strategy_test.php
@@ -226,7 +226,7 @@ class core_calendar_raw_event_retrieval_strategy_testcase extends advanced_testc
         $events = $retrievalstrategy->get_raw_events([$group12student->id], $groups, [$course->id]);
         $this->assertCount(1, $events);
         $event = reset($events);
-        $this->assertEquals('Assignment 1 due date - Group B override', $event->name);
+        $this->assertEquals('Assignment 1 due date - Group A override', $event->name);
 
         // Get events for user that belongs to group A and has no user override events.
         $this->setUser($group1student);
diff --git a/lib/db/upgrade.php b/lib/db/upgrade.php
index 007594f52ea..3b9f6d8c992 100644
--- a/lib/db/upgrade.php
+++ b/lib/db/upgrade.php
@@ -2575,6 +2575,10 @@ function xmldb_main_upgrade($oldversion) {
         $record->nextruntime = $nextruntime;
         $DB->insert_record('task_adhoc', $record);
 
+        // This same task is queued again in a later step, but if we already queue it here
+        // then there is no need to queue it again. We use this flag in the second step.
+        $refresheventsadhocadded = true;
+
         // Main savepoint reached.
         upgrade_main_savepoint(true, 2017030700.00);
     }
@@ -2834,5 +2838,24 @@ function xmldb_main_upgrade($oldversion) {
         upgrade_main_savepoint(true, 2017041801.00);
     }
 
+    if ($oldversion < 2017042600.01) {
+        // If the previous step didn't execute and queue the task.
+        if (!isset($refresheventsadhocadded)) {
+            // Create adhoc task for upgrading of existing calendar events.
+            $record = new \stdClass();
+            $record->classname = "\\core\\task\\refresh_mod_calendar_events_task";
+            $record->component = 'core';
+
+            // Next run time based from nextruntime computation in \core\task\manager::queue_adhoc_task().
+            $nextruntime = time() - 1;
+            $record->nextruntime = $nextruntime;
+            $DB->insert_record('task_adhoc', $record);
+
+        }
+
+        // Main savepoint reached.
+        upgrade_main_savepoint(true, 2017042600.01);
+    }
+
     return true;
 }
diff --git a/mod/assign/lib.php b/mod/assign/lib.php
index d63e2d23b46..30c472c9ff0 100644
--- a/mod/assign/lib.php
+++ b/mod/assign/lib.php
@@ -127,7 +127,8 @@ function assign_refresh_events($courseid = 0) {
         $assignment->update_calendar($cm->id);
 
         // Refresh the calendar events also for the assignment overrides.
-        $overrides = $DB->get_records('assign_overrides', ['assignid' => $assign->id], '', 'id, groupid, userid');
+        $overrides = $DB->get_records('assign_overrides', ['assignid' => $assign->id], '',
+                                      'id, groupid, userid, duedate, sortorder');
         foreach ($overrides as $override) {
             if (empty($override->userid)) {
                 unset($override->userid);
diff --git a/mod/lesson/lib.php b/mod/lesson/lib.php
index 80e904d58bb..c0bee742793 100644
--- a/mod/lesson/lib.php
+++ b/mod/lesson/lib.php
@@ -243,7 +243,7 @@ function lesson_update_events($lesson, $override = null) {
 /**
  * Calculates the priorities of timeopen and timeclose values for group overrides for a lesson.
  *
- * @param int $lessonid The quiz ID.
+ * @param int $lessonid The lesson ID.
  * @return array|null Array of group override priorities for open and close times. Null if there are no group overrides.
  */
 function lesson_get_group_override_priorities($lessonid) {
@@ -268,8 +268,8 @@ function lesson_get_group_override_priorities($lessonid) {
         }
     }
 
-    // Sort open times in descending manner. The earlier open time gets higher priority.
-    rsort($grouptimeopen);
+    // Sort open times in ascending manner. The earlier open time gets higher priority.
+    sort($grouptimeopen);
     // Set priorities.
     $opengrouppriorities = [];
     $openpriority = 1;
@@ -277,8 +277,8 @@ function lesson_get_group_override_priorities($lessonid) {
         $opengrouppriorities[$timeopen] = $openpriority++;
     }
 
-    // Sort close times in ascending manner. The later close time gets higher priority.
-    sort($grouptimeclose);
+    // Sort close times in descending manner. The later close time gets higher priority.
+    rsort($grouptimeclose);
     // Set priorities.
     $closegrouppriorities = [];
     $closepriority = 1;
diff --git a/mod/lesson/tests/lib_test.php b/mod/lesson/tests/lib_test.php
index 1b32f7cee87..f0e8ef10266 100644
--- a/mod/lesson/tests/lib_test.php
+++ b/mod/lesson/tests/lib_test.php
@@ -74,13 +74,13 @@ class mod_lesson_lib_testcase extends advanced_testcase {
 
         $openpriorities = $priorities['open'];
         // Override 2's time open has higher priority since it is sooner than override 1's.
-        $this->assertEquals(1, $openpriorities[$override1->available]);
-        $this->assertEquals(2, $openpriorities[$override2->available]);
+        $this->assertEquals(2, $openpriorities[$override1->available]);
+        $this->assertEquals(1, $openpriorities[$override2->available]);
 
         $closepriorities = $priorities['close'];
         // Override 1's time close has higher priority since it is later than override 2's.
-        $this->assertEquals(2, $closepriorities[$override1->deadline]);
-        $this->assertEquals(1, $closepriorities[$override2->deadline]);
+        $this->assertEquals(1, $closepriorities[$override1->deadline]);
+        $this->assertEquals(2, $closepriorities[$override2->deadline]);
     }
 
     /**
diff --git a/mod/quiz/lib.php b/mod/quiz/lib.php
index 7ce1e229afe..d783f987c27 100644
--- a/mod/quiz/lib.php
+++ b/mod/quiz/lib.php
@@ -1352,8 +1352,8 @@ function quiz_get_group_override_priorities($quizid) {
         }
     }
 
-    // Sort open times in descending manner. The earlier open time gets higher priority.
-    rsort($grouptimeopen);
+    // Sort open times in ascending manner. The earlier open time gets higher priority.
+    sort($grouptimeopen);
     // Set priorities.
     $opengrouppriorities = [];
     $openpriority = 1;
@@ -1361,8 +1361,8 @@ function quiz_get_group_override_priorities($quizid) {
         $opengrouppriorities[$timeopen] = $openpriority++;
     }
 
-    // Sort close times in ascending manner. The later close time gets higher priority.
-    sort($grouptimeclose);
+    // Sort close times in descending manner. The later close time gets higher priority.
+    rsort($grouptimeclose);
     // Set priorities.
     $closegrouppriorities = [];
     $closepriority = 1;
diff --git a/mod/quiz/tests/lib_test.php b/mod/quiz/tests/lib_test.php
index a260a05522b..8a54c36eb93 100644
--- a/mod/quiz/tests/lib_test.php
+++ b/mod/quiz/tests/lib_test.php
@@ -489,13 +489,13 @@ class mod_quiz_lib_testcase extends advanced_testcase {
 
         $openpriorities = $priorities['open'];
         // Override 2's time open has higher priority since it is sooner than override 1's.
-        $this->assertEquals(1, $openpriorities[$override1->timeopen]);
-        $this->assertEquals(2, $openpriorities[$override2->timeopen]);
+        $this->assertEquals(2, $openpriorities[$override1->timeopen]);
+        $this->assertEquals(1, $openpriorities[$override2->timeopen]);
 
         $closepriorities = $priorities['close'];
         // Override 1's time close has higher priority since it is later than override 2's.
-        $this->assertEquals(2, $closepriorities[$override1->timeclose]);
-        $this->assertEquals(1, $closepriorities[$override2->timeclose]);
+        $this->assertEquals(1, $closepriorities[$override1->timeclose]);
+        $this->assertEquals(2, $closepriorities[$override2->timeclose]);
     }
 
     public function test_quiz_core_calendar_provide_event_action_open() {
diff --git a/version.php b/version.php
index 92ad9dcb552..81dd163899e 100644
--- a/version.php
+++ b/version.php
@@ -29,7 +29,7 @@
 
 defined('MOODLE_INTERNAL') || die();
 
-$version  = 2017042600.00;              // YYYYMMDD      = weekly release date of this DEV branch.
+$version  = 2017042600.01;              // YYYYMMDD      = weekly release date of this DEV branch.
                                         //         RR    = release increments - 00 in DEV branches.
                                         //           .XX = incremental changes.