Zombies Troubleshoot

Today got 2 COBK zomibies on our ent server(as400), we are on 9.1 TR9205

For both zombie COBK, same thread failed at same time with the same call stack.

But there are no ERROR message in the log. Technically there is always an error log right before the generating call stack entry for the thread, which is not the case here.

Zombie 1-

147954/6771 WRK:Init Remote Env Token           Mon Jul 31 06:52:03.775488     jdecallstk.c453
Generating Call Stack for PID 147954 from PID 147954 with 7 active threads out of 7 total threads available

Zombie 2-147796/216 WRK:Init Remote Env Token            Mon Jul 31 06:52:03.775488     jdecallstk.c453
Generating Call Stack for PID 147796 from PID 147796 with 7 active threads out of 7 total threads available