ATT Gateway and RBR20 Issues

I've posted several times regarding the ongoing issues I'm having with my Arris ATT Gateway and my Orbi RBR20 Router and Satellite. Now I'm at a loss.

For 2 months, I had the Gateway in IP Passthrough mode (ATT does not allow Bridge mode), but I still had the WiFi signals on. All was fine. The ATT Gateway was broadcasting a WiFi signal, but I never used it or connected any devices to it. I only used my Orbi WiFi network.

Last week, things started happening:

-I could not access orbilogin.net/com

-Not all of my connected devices showed up in the Orbi admin app or on the browser admin page

So I talked to ATT, and they turned off the WiFi radios (per a suggestion someone made here, to get rid of my Double NAT situation).

All was good.

Then a few days later I started to get buffering on my AppleTV, and a Speedtest revealed super slow speeds on my AppleTV. All other devices seemed fine. Also, the ATT app would show me as offline for a few seconds when I was online, then woiuld update to online.

I called ATT again and they turned the WiFi radios back on as a way to fix the connection status issue. But they still kept me in Passthrough mode.

Now, the buffering issue is fixed (I think), but I am back to not seeing all my connected devices. Plus, I'm seeing a new unknown device. And the ATT app still has the offline/online problem.

What I'd be incredibly grateful for is for someone to tell me exactly what to tell ATT to do as far as the settings in Passthrough mode that will be optimal for my Orbi system. And then, what settings to use for my Orbi.

Thank you!