I had the same problem. RUT955 could not connect to AP AC Pro and AP AC LR with the existing SSID.
With a cheap TP AccessPoint and to a Mobile Phone Hotspot it worked straight away.
then I created a new WiFi network (Pasch Kfz) on just one access point in the standard, actually just kept clicking yes yes yes
2.4Ghz only, no 5Ghz, automatic channel, 40MHz bandwidth, WPA2
After that, all previously created client mode WiFi networks in RUT will be deleted.
Then Scan, WiFi Pasch Kfz selected and added. Waited a minute and the RUT was connected to the UniFi network, internet was running.