If you are experimenting issues with the CPU usage on a unifi controller, you might read the related article on ui support.
Basically, append these lines to /usr/lib/unifi/data/system.properties to enable advanced garbage collection and
increase the memory the java process will use (in Mb). If this space is not enough, java will overuse the CPU causing the app to freeze.
unifi.G1GC.enabled=true
unifi.xms=6144
unifi.xmx=6144
Then make a sudo service unifi restart.
Use free -hand top to monitor the app. You can also view the server log with
´´´ sudo tail -f /var/log/unifi/server.log ´´´