dump the logs of pgag and ccag for pg and cc and check the logs. for your reference you will see the low and high priority messages exchanges between router and pg and router receiving the ACK back from PG.
Router sending low priority messaged to PG:
Queuing low priority roll-forward to PG01 (seq 40010000)
PG receiving low priority messaged from designated cc side.
PG1A-pgag Message Trace: DMP sending low priority message to Central Controller side A