best approach is to try and build up a test case from what you know to see if you can isolate or reproduce the problem.
I see two potential candidates for generating an imbalance on memory usage.
1) the DLQ discarding messages
2) the message expiry processing
It may be possible to build a test case that introduces one at a time to see if you can reproduce.
Introducing a lower memory limit for your test case will help reproduce in a shorter period of time.
hi..thanks tully..i also tried your tips...it worked fine with my issue.