The config is quite default, we just configured our queues. There is no Job scheduled at all, please see screenshot. Please note as mentioned earlier it takes a number of days (8-20) until the issue happens.

Also I would like to note that it doen't matter which of both nodes/servers is active/standby, it happend in both cases.
I can send you routerconfig.xml and/or HeapDump if you need for further analyses.
Best regards,
Michael