I've reproduce it by this steps:

1. Spawn 2 instances of broker
2. Sent 100 non-durable messages + 100 durable messages to Broker#2
3. Scaledown

At this point, Drain pod has been spawned which has produced the attached log. As it can be seen in the log, the Drainer has failed to actually connect to Broker #1, however it has reported a success & has removed the PVC/PV (so durable messages are gone).