These U1304 abends typically occur when the external archive or external extract subtasks of CA Dispatch lose their communication link with/to the CA Dispatch MAIN region.
You can identify and confirm this communication link loss as being the cause of the problem via the existence of the following message(s) appearing in the logs prior to the U1304 abend occurring:
DC980041 - ARBGDB - 0069 STATUS - CV NOT PRESENT, TASK ABENDING
DC980042 - ARBGEXDB - 0069 STATUS - CV NOT PRESENT, TASK ABENDING
The cause of the communication disconnect may have been the result of some kind of contention problem between the external subtask and the main CA Dispatch region. Or, contention with a CA Dispatch batch utility job running at a time when the ARCHIVE or EXTRACT subtasks of CA Dispatch needed to be stopped first, before running the utility job.
It may have also been the result of a problem in the MAIN CA Dispatch region itself. For example, if someone brought the MAIN region DOWN, issued a CANCEL command, or if it abended.
If you receive one of these U1304 abends, check the MAIN CA Dispatch regions logs and see if there were any problems with the MAIN CA Dispatch region around the time the external subtask abended. You will likely find that the MAIN region was brought down.
In any case, the appropriate resolution to the U1304 abend would be to RESTART the external subtask. Depending on what you find in the MAIN CA Dispatch regions logs, you might also want to consider recycling the MAIN region before restarting the external tasks.