RBR750 In AP Mode

Factory reset has been tried multiple times...

Size of house is irrelevant as it happens with the Router sitting on my desk where it is being configured.

The modem is Optimum's cable modem (Arris TM1602 which we've had for at least 5 years now), and even tried when I tested out TMobile's 5G modem.

Tried all different channels...

I have tried rebuilding from scratch (unfortunately with this firmware) without using any satellites.  This starts to happen before I even connect one...

Tons of nearby neighbors, but it is the same amount as when I'm in router mode... 

As mentioned, purchased a new one and as soon as I put into AP mode, it happened all over again so I returned the new one...   It worked until it was upgraded, and there is no possibility to downgrade (the new router had the same issue).  

Router mode everything works perfectly (took a while and that is where I have to leave it now until they fix it), but as soon as I go to AP mode, WiFi goes in and out.  Doesn't matter what device (iPhones, iPads, Windows laptop, iMac, and MacBooks) as it is always the same result of the WiFi dropping.  The SSID actually disappears, then reappears, then disappears, etc - around every 20 seconds or so...  Tried some of the other oddball settings recommended from other threads, but nothing worked...  

Giving up on these - unless there is a resolution, the next purchase won't be Netgear...