We had a long, drawn out support ticket with Unifi about this. In the end they said this incredibly high CPU usage was expected behaviour
Much of the saga is chronicled here:
https://community.ui.com/questions/...CPU/ca8d4f20-ec87-4c38-aa04-33ac05f1fb2fIt turned out our workaround of /usr/bin/cpulimit -b -l 50 -e /usr/lib/jvm/java-8-openjdk-amd64/jre/bin/java caused a few other issues such as occasional controller lockups and lack of client stats when viewing a site. (black screen when trying to view client device list)
This morning we upgraded the controller software to 6.5.53 and happened to notice an option to turn off "Analytics & Improvements" under Network Application>Console Settings. The Unifi upgrade didn't make much of a change even after we gave the CPU a chance to settle down. However, within minutes of turning off "Analytics & Improvements" our CPU usage on the AWS t3a.xlarge instance went from around 45% to 2.5% and has been there for a half hour! We may be jumping the gun but this option appears to be the single source of all the nasty Java CPU usage.