Messages may accumulate in the MQ Dead Letter Queue due to valid MQ errors. This situation commonly occurs when the Connection Manager disconnects and reconnects. During this process, any temporary reply queues that were in use at that time may be removed. As a result, reply messages cannot be delivered to the intended reply queues and are instead routed to the Dead Letter Queue.
How to resolve this issue
You can resolve this issue using one of the following approaches:
Stop the Connection Managers before performing any system reboot.
Use predefined permanent queues instead of temporary dynamic queues.
In some environments, using predefined permanent queues may require an upgrade or application of the appropriate hotfix to the M6WMQ component. After applying the required fix, you should be able to use permanent queues, which prevents replies from being routed to the Dead Letter Queue during reconnection scenarios.