Error acknowledging messages

I am running some tests on the broker using our performance client and I noticed some errors on the logs.

Our logs are full of messages stating that it failed to acknowledge the message due to a missing reference (see ack-error.log).
This seems to build up over time and reduce the broker throughput. After some time, the broker hangs and prints an error about failing to finish waiting for executors (see executors-warnings.log) and ends up hanging and printing a thread dump (see thread-dump.log).

Some comments:

• we did not have such problem with A-MQ 6.
• this problem seems to be triggered only by the performance client. I don't have the latest version my COPR, but I can provide compilation instructions if you need it to reproduce the issue.