diff --git a/lib/classes/task/manager.php b/lib/classes/task/manager.php
index f81ca5ea086..091974bfb07 100644
--- a/lib/classes/task/manager.php
+++ b/lib/classes/task/manager.php
@@ -479,7 +479,7 @@ class manager {
      * relative order of tasks queued by timestamp.
      *
      * @param array $records array of task records
-     * @return void
+     * @param array $records array of same task records shuffled
      */
     public static function ensure_adhoc_task_qos(array $records): array {
 
@@ -508,6 +508,7 @@ class manager {
         $qos = []; // Our new queue with ensured quality of service.
         $seed = $count % $limittotal; // Which task queue to shuffle from first?
 
+        $move = 1; // How many tasks to shuffle at a time.
         do {
             $shuffled = 0;
 
@@ -529,11 +530,16 @@ class manager {
                     $seed += 1;
                     continue;
                 }
-                $task = array_splice($queues[$type], 0, 1);
-                $qos = array_merge($qos, $task);
+                $tasks = array_splice($queues[$type], 0, $move);
+                $qos = array_merge($qos, $tasks);
 
                 // Stop if we didn't move any tasks onto the main queue.
-                $shuffled += count($task);
+                $shuffled += count($tasks);
+            }
+            // Generally the only tasks that matter are those that are near the start so
+            // after we have shuffled the first few 1 by 1, start shuffling larger groups.
+            if (count($qos) >= (4 * count($limits))) {
+                $move *= 2;
             }
         } while ($shuffled > 0);
 
@@ -550,11 +556,6 @@ class manager {
      */
     public static function get_next_adhoc_task($timestart) {
         global $DB;
-        $cronlockfactory = \core\lock\lock_config::get_lock_factory('cron');
-
-        if (!$cronlock = $cronlockfactory->get_lock('core_cron', 10)) {
-            throw new \moodle_exception('locktimeout');
-        }
 
         $where = '(nextruntime IS NULL OR nextruntime < :timestart1)';
         $params = array('timestart1' => $timestart);
@@ -562,6 +563,11 @@ class manager {
 
         $records = self::ensure_adhoc_task_qos($records);
 
+        $cronlockfactory = \core\lock\lock_config::get_lock_factory('cron');
+        if (!$cronlock = $cronlockfactory->get_lock('core_cron', 10)) {
+            throw new \moodle_exception('locktimeout');
+        }
+
         foreach ($records as $record) {
 
             if ($lock = $cronlockfactory->get_lock('adhoc_' . $record->id, 0)) {
diff --git a/lib/tests/task_manager_test.php b/lib/tests/task_manager_test.php
index cb99cf68211..b3007e9a265 100644
--- a/lib/tests/task_manager_test.php
+++ b/lib/tests/task_manager_test.php
@@ -50,6 +50,12 @@ class core_task_manager_testcase extends advanced_testcase {
                     (object)['id' => 7, 'classname' => '\tool_dataprivacy\task\process_data_request_task'],
                     (object)['id' => 8, 'classname' => '\tool_dataprivacy\task\process_data_request_task'],
                     (object)['id' => 9, 'classname' => '\tool_dataprivacy\task\process_data_request_task'],
+                    (object)['id' => 10, 'classname' => '\tool_dataprivacy\task\process_data_request_task'],
+                    (object)['id' => 11, 'classname' => '\tool_dataprivacy\task\process_data_request_task'],
+                    (object)['id' => 12, 'classname' => '\tool_dataprivacy\task\process_data_request_task'],
+                    (object)['id' => 13, 'classname' => '\tool_dataprivacy\task\process_data_request_task'],
+                    (object)['id' => 14, 'classname' => '\tool_dataprivacy\task\process_data_request_task'],
+                    (object)['id' => 15, 'classname' => '\tool_dataprivacy\task\process_data_request_task'],
                 ],
                 [
                     (object)['id' => 1, 'classname' => '\core\task\asynchronous_backup_task'],
@@ -59,8 +65,14 @@ class core_task_manager_testcase extends advanced_testcase {
                     (object)['id' => 3, 'classname' => '\core\task\asynchronous_backup_task'],
                     (object)['id' => 9, 'classname' => '\tool_dataprivacy\task\process_data_request_task'],
                     (object)['id' => 4, 'classname' => '\core\task\asynchronous_backup_task'],
+                    (object)['id' => 10, 'classname' => '\tool_dataprivacy\task\process_data_request_task'],
                     (object)['id' => 5, 'classname' => '\core\task\asynchronous_backup_task'],
                     (object)['id' => 6, 'classname' => '\core\task\asynchronous_backup_task'],
+                    (object)['id' => 11, 'classname' => '\tool_dataprivacy\task\process_data_request_task'],
+                    (object)['id' => 12, 'classname' => '\tool_dataprivacy\task\process_data_request_task'],
+                    (object)['id' => 13, 'classname' => '\tool_dataprivacy\task\process_data_request_task'],
+                    (object)['id' => 14, 'classname' => '\tool_dataprivacy\task\process_data_request_task'],
+                    (object)['id' => 15, 'classname' => '\tool_dataprivacy\task\process_data_request_task'],
                 ],
             ],
             // The same lopsided queue but now the first item is gone.
@@ -147,6 +159,20 @@ class core_task_manager_testcase extends advanced_testcase {
         ];
     }
 
+    /**
+     * Reduces a list of tasks into a simpler string
+     *
+     * @param array $input array of tasks
+     * @return string list of task ids
+     */
+    function flatten($tasks) {
+        $list = '';
+        foreach ($tasks as $id => $task) {
+            $list .= ' ' . $task->id;
+        }
+        return $list;
+    }
+
     /**
      * Test that the Quality of Service reordering works.
      *
@@ -159,6 +185,11 @@ class core_task_manager_testcase extends advanced_testcase {
     public function test_ensure_adhoc_task_qos(array $input, array $expected) {
         $this->resetAfterTest();
         $result = \core\task\manager::ensure_adhoc_task_qos($input);
+
+
+        $result = $this->flatten($result);
+        $expected = $this->flatten($expected);
+
         $this->assertEquals($expected, $result);
     }