For anyone interested in upgrading to 6.0.20, there are some issues reported, so it is not advisable to upgrade until Ubiquiti comes to a fix.
I am linking below some information I have found (admins, please let me know if I should remove those, I am in no way affiliated with the youtube channel, just though it may provide some insights on the issues found).
https://community.ui.com/questions/Broadcast-storm-after-Unifi-controller-upgrade-to-6-0-20/0b924047-0632-4304-bada-4158a0a5349e
https://www.youtube.com/watch?v=37Bl4yvIwqA
Hope Unifi comes with a solution soon.
Regards
EDIT:
Unifi has come with an updated version: 6.0.22 with bugfixes.
https://community.ui.com/releases/UniFi-Network-Controller-6-0-22/910ceffc-f0e9-4518-86c1-df5eeee34695
Regards