I have 2x of the AX92U routers, they are connected with a wireless backhaul for the mesh. They are spaced about 15 feet apart on the 1 first floor of the house and the router says its a great signal. They are covering about 1900 sq ft and I have about 20ish wifi clients connected. I seems to mostly have issues with the 5Ghz-1 but it also happens on the 2.4Ghz. Basically after 1-2 days (sometimes even just a few hours) a device that is on wifi will just disconnect and fail to get a new IP address. Sometimes rebooting that device fixes it, other times it doesnt however it starts to kinda cascade where more and more devices stop connecting over the next few hours and eventually the whole wifi mesh craps out. A reboot resolves the issue and currently I have my router set to reboot every morning. Ive tried the most recent 3 firmwares and the beta firmware which I am currently on. Prior to setting up the mesh when I had just 1 router, things were working fine and my wireless was stable, it just was weak at a few spots in the house so I got the 2nd to switch to a mesh and hopefully have full coverage.
update: after updating the firmware I do a factory reset for both the main router and the node, then i get the main router configured so I can login to it, then add the mesh and finish the configuration. I have mostly default settings and only add a few things like some port forwarding stuff.