Application Engine programs only stuck at queued

You may find that only application engine programs are stuck at queued while other processes (SQRs, crystals etc) run to success. This typically happens due to processes blocking the process scheduler queue. Check the process scheduler/master process scheduler logs. You might see something like this:

Checking Process cancels...
(NET.113): Client ChkAeStatus3 service request succeeded
Process 2319373 is still running as Session ID 19955
(NET.113): Client ChkAeStatus1 service request succeeded
Process 2319395 is still running as Session ID 19946
(NET.113): Client ChkAeStatus2 service request succeeded
Process 2319404 is still running as Session ID 19950
Application Engine : 3:3
Requests found in Process Request table 3

This indicates that the three process instances, 2319373, 2319395 and 2319404 are all running. As there is a maximum of 3 application engine programs that can run at any one time and there are currently 3 running, all other application engine programs requested will remained at queued. However, the three process instances may not actually be running. If this is the case, these will need to be manually stopped, for example with a process scheduler restart and perhaps by manually killing the processes on the process scheduler server if required.