Interesting 😕 are you seeing connectivity issues - client not being able to communicate even if reported to be connected (on device and in Unleashed UI)? 5GHz clients all report poor signal strength regardless of distance to AP. Currently running with wifi-6 disabled, which up until two days ago seemed to had a positive impact.
Having same/similar symptoms.
Previous Unifi AP AC Lite worked perfectly, but now on R550 lot of 5GHz devices have "poor" 5Ghz signal - even ones that are 2-3m away from AP with clear line of sight with no other wifi in house.
Device has installed Unleashed 184.108.40.206.212 firmware.