We hit this problem on Workplace but I think I can find examples in LMS as well.

There are some rare cases when the report definition depends on the current user. In case of Workplace, we add a tenant subquery to the "User list" datasource, for example so the same report for different users has different SQL and produces different results.

When we create a schedule for such report, the datasource definition is created for the first user in the batch and then re-used for all other users, even if the schedule setting is to generate a new report for each user.

As a very simple solution I can suggest to add a user id in the cache key. I'll try to come up with some testing instructions or unittests for this in LMS.

diff --git a/reportbuilder/classes/manager.php b/reportbuilder/classes/manager.php

index 143a7cd20ef..cebfa5b775d 100644

--- a/reportbuilder/classes/manager.php

+++ b/reportbuilder/classes/manager.php

@@ -50,7 +50,8 @@ class manager {

      * @throws source_unavailable_exception

      */

     public static function get_report_from_persistent(report $report, array $parameters = []): base {

-        $instancekey = $report->get('id');

+        global $USER;

+        $instancekey = $report->get('id') . ':' . $USER->id;

         if (!array_key_exists($instancekey, static::$instances)) {

             $source = $report->get('source');