OK I figured it out.

I used the same ThreadExecutor for the int-amqp:inbound-channel-adapter to handle incoming job request and for the tasklet adapter itself. Would not be a problem however I set the queue on the TaskExecutor to 0 to prevent of building up any waiting jobs (the MQ is for that) and when the Job wanted to perform, and the thread pool had been exhausted, it probably rejected the incoming calls (but no rejection policy had been set). Do I understand that right?