AEM LTS (flush agents)

I’m practicing an upgrade from AEM 6.5.21 on-prem Java 11 to AEM LTS (6.6.3) on-prem Java 21 - things seem to have gone pretty smoothly, my replication agents (on author) test successfully and I can replicate pages to the publish instance. 

I was looking at my flush agent setup and trying to replicate it from the author to a publish instance and it did not replicate (the UI just spun). 

I checked enabled for this agent and on saving the flush agent, this appears in the author log: 

13.10.2026 12:14:42.136 *INFO* [sling-oak-observation-20] com.day.cq.replication.impl.ConfigManagerImpl Configuration for agent at /etc/replication/agents.publish/<agent-name> is not active.

I can deactivate the flush agent but activate just hangs. 

I tried reverting to Java 17 on the LTS instance but that did not change things.

I am going to try packaging the agent for install on publish the instance.

Installing as a package seems to be working? Not fully tested but the view log and test links in agent config on the publish instance seem to work. Is this expected in the newer AEM?

Thanks for any assistance.