application stuck in rt_put_prio

/* Search for an entry in the list */
  while ((p_CB2 != NULL) && (prio <= p_CB2->prio)) {
    p_CB = (P_XCB)p_CB2;
    p_CB2 = p_CB2->p_lnk; <--- sometimes stuck here
  }
  /* Entry found, insert the task into the list */
  p_task->p_lnk = p_CB2;
  p_CB->p_lnk = p_task;
  if (sem_mbx) {
    if (p_CB2 != NULL) {
      p_CB2->p_rlnk = p_task;
    }
    p_task->p_rlnk = (P_TCB)p_CB; <----stuck here
  }
  else {
    p_task->p_rlnk = NULL;
  }
}

I have an issue where about after an 2 - 3 hours of running the CMSIS locks up in the rt_list.c
very rarely but sometimes the processor hard faults and doing a stack trace points to the same rt_list.c function rt_put_prio.

Am I encountering a deadlock?
The only other thing I can think of is one of my functions is changing the memory this function is using to manage the priority list?

This is on a cortex M0+ processor with 9 total threads
I have configured all the threads with the same priority. I am using two mailbox's
My round robin timer is 10 ticks, any other timer and the CMSIS only runs for 10 seconds and then locks up. Tried 5 ticks and 10 ticks.

Any help would be greatly appreciated.