В документации описано:
queue_qos0_messages [ true | false ]
Set to true to queue messages with QoS 0 when a persistent client is disconnected. When bridges topics are configured with QoS level 1 or 2 incoming QoS 0 messages for these topics are also queued. These messages are included in the limit imposed by max_queued_messages. Defaults to false.
Но у вас вообще qos-level задан 2.