If you are getting a queue, your QoS is already set to 1 so we don’t have to worry about that. What SAP system are you using and perhaps I can help find out if the session can be changed or not? It is a boolean, so sometimes it is just a checkbox like in SAP Plant Connectivity.
Clean Session if Connection Was Interrupted … If you select the checkbox, any messages that have been missed during an interruption to the connection are not sent when the connection is restored. If you do not select the checkbox, and the connection is interrupted, the MQTT server sends all missed messages as soon as the connection has been restored.