When selecting "all" from the Warden -> Queue select list on the queue page you get the error:
Status: 500 - Internal Server Error
TypeError [ 0 ]: Queue::list(): Argument #1 ($queue_name) must be of type string, null given
called in /opt/psa/admin/plib/modules/warden/library/application/classes/Model/Queue.php on line 28
This has been fixed in the latest version of Warden. You can upgrade to it using the command:
plesk bin extension --install-url https://www.danami.com/clients/downloads/warden.zip