So I recently purchased a pair of Deco BE63 routers from Amazon. Main reason was to use the home wiring Ethernet as backhaul as my previous Eero's started to fail miserably due to some combination of software updates and maybe neighbors getting more aggressive with their own WiFi signal (live in townhouse, can usually see at least 12 other SSIDs if not more at any given time).

General setup is: main unit is in my office upstairs SW corner of three story townhouse, plugged into Ethernet jack that goes directly to Verizon FIOS router (G3100). Second unit is first floor, NW corner, with a problematic wall with lots of AC ductwork in between (which is what was breaking the Eeros, because I have another requirement to not have any visible wires from my wife), by another Ethernet jack also ending up on the FIOS router.

The wired backhaul failed, probably because of the FIOS router not allowing the port-to-port broadcast to work. I briefly tried to put a TPLink 5 port smart switch in between them by the FIOS router (which is in a metal box in the garage, builder's choice) but that broke a whole lot of stuff, not sure why. Ultimately I want to use that for port mirroring to another raspberry Pi5 running network monitoring software but that's a future plan. The second unit Ethernet jack and cable has been confirmed to work just fine (using a USB-C to Ethernet adapter on my iPhone; it gets an IP from the FIOS router and accesses the internet etc.).

Wired network is range A (call it 192.168.1.0/24), wireless network is range B (call it 192.168.80.0/26), which should be fine. The primary Deco has its dynamic WAN IP in range A. They do share the same physical Ethernet wiring (in that I have some Ethernet and wifi devices on the range A wired network and wireless range B network, and of course at least the primary Deco has that WAN IP and the LAN IP it being a router).

I'm still having a lot of problems with stability, mainly on devices that support WiFi6+ (my iPhone 15 Pro and iPad Pro M2 being the ones I use most and notice it the most). In fact, I had to turn off WiFi to get the reCAPTCHA to work.

But my main question is about whether the WiFi Router mode really doesn't like being behind a FIOS router, and if Access Point should be used instead. I'm struggling to understand why it would care how many devices it goes through to get to the services on the internet as long as routing is there, but clearly something else is going on. I'll probably try Access Point mode this weekend when it's not as critical to have a working network for a while, but am wondering if anyone has WiFi Router working in this scenario.

Thanks.

Michael