X4S R7800 Router WiFi Stops Working After Random Periods - Cannot Turn Back On

Thanks yet again for this informative and helpful response!

I can confirm that 5G was never set to a DSF channel, but on 40 and 44 when manual, and on Auto otherwise. 2G was tried on Auto, as well as 6 and 11. These channels specified above should be good to go, so I sadly have to eliminate this possibility too.

As for new equipment being installed. No Chromecast in the home, although I do have two Alexa/Amazon Echo Dot devices in use, and a WiFi Yeelight lamp. Crucially, they all were working fine - the router did not have this WiFi turn-off problem from the beginning but only developed it gradually. No device had changed on my network for a couple of months before the problems begun. Crucially, I also tried eliminating potential problematic devices by only allowing devices to connect to the router in a "vet" process:

1. I would connect one device. Let the router work with that one for a while.

2. Then add one more, etc etc.

I do not believe I verified a single device causing the problem. If anything the problem seemed random, and happens regardless of device(s) connected to the router.

I have proceeded to ask for an RMA. I really hoped this is something the forum has heard of before, to avoid the hassle of a return and replacement - but so long as that solves my problem I will be okay!