The communication subsystem let to a failed ad hoc task which had this output:

Execute adhoc task: core_communication\task\update_room_membership_task
Adhoc task id: 12877912
Adhoc task custom data:{{{}

{}}}... started 14:40:37. Current memory use 18.3 MB.
Debugging increased temporarily due to faildelay of 86400
... used 1 dbqueries
... used 0.013222932815552 seconds
Adhoc task failed: core_communication\task\update_room_membership_task,Fehler in der Kodierung gefunden, den nur Programmierer/innen korrigieren können: room features are not supported by the provider
Backtrace:

• line 531 of /communication/classes/processor.php: call to core_communication\processor->require_room_user_features()
• line 42 of /communication/classes/task/update_room_membership_task.php: call to core_communication\processor->get_room_user_provider()
• line 519 of /lib/classes/cron.php: call to core_communication\task\update_room_membership_task->execute()
• line 348 of /lib/classes/cron.php: call to core\cron::run_inner_adhoc_task()
• line 148 of /admin/cli/adhoc_task.php: call to core\cron::run_adhoc_task()

Line 531 calls the function require_room_user_features() which in case should throw a different exception message.