To eliminate my AP, I have enabled WiFi on my FRITZ!Box 7530. I created a 2.4GHz SSID just for the Nuki, and am getting the exact same behaviour. Connects for a few minutes, drops, and fails to reconnect.
TBH, I’m not really convinced that I should have to join a beta program to resolve a core issue where the device is just not functioning correctly.
Typically joining such a program means accepting limited support, which does not seem acceptable in this case.