RAX200 in AP mode inaccessible, had to reset

Does AP mode truly work on the RAX200? I put mine into AP mode (keeping defaults), and it immediately stopped working for all intents and purposes. Wired clients could not get an IP address (even though the WAN port was connected to the main router providing DCHP), and although the RAX's wireless networks were still visible, I could no longer connect to any of them from any client (they'd struggle and eventually time out). In addition, no amount of manual IP setting would allow wired clients to see the RAX. When I looked at the other router (which was providing DHCP and the internet connection for the AP mode RAX200), I could see the RAX would be assigned an IP address for a little while, and then disappear from the network. After an hour of flailing with it, I finally gave up and hard-reset the RAX, as I couldn't connect no matter what I did. It's working again (_not_ in AP mode), but I'm wondering what could have gone wrong. Any ideas from those who have done this?

For those who are wondering why in the world I would put the RAX200 into AP mode, I'm trying to avoid a double-NAT situation. My home is wired in a troublesome way, and the best location for a Wifi router is far from where the internet comes in (the latter being well-connected to wired jacks throughout the house). As a result, I have a separate router where the internet enters the house (providing a firewall and acting as a switch for various outlets/devices), and it provides a WAN connection via MoCA to the centrally-located RAX200, which is my main wireless router. Unfortunately, with there is no way to connect wired clients to the RAX, which is why I have two routers, and with the double-NAT setup, a couple of my devices don't work. Is there another way to make this setup work without the complexity?