U-verse not available at this time loop

Try restarting the WAP.  

As I'd said in the original post, I reset the twice WAP already, once when resetting all the receivers and the DVR, and once when I reset all the receivers and the DVR and the gateway. But... just in case, I tried resetting the WAP by itself, and nothing changed.

FWIW, I swapped the locations of the working receiver and the non-working receiver, in case location was the reason for failure... and the working receiver kept working and the non-working receiver kept shirking. I guess I'll get to have fun talking to ATT.

They’ll probably ship you a replacement settop box given what you’ve stated above.  
If I had this happen after rebooting the home network, I’d force the settop box through a factory reset and then let it reload code from the server while it’s hardwired connected to the gateway.  Afterwards it will usually connect to the WAP fine.  

OK, I tried resetting and connecting directly to the gateway and waiting. When connected back to the TV, the receiver started it reboot loop again. I'll try contacting AT&T. Thanks for the input.

If you connected the settop box to gateway via Ethernet, did you perform the factory reset first?   Plug and unplug settop box three times spaced by several seconds?

No. I tried unplugging the receiver for a good long time, plugging it back in, then plugging in the ethernet cable from the gateway, waiting a bit and then resetting it by pushing the power button until the lights cycled through, as this last bit was what I found kicking around the internet for 'resetting uverse receiver'. I'll try this new technique later.

@wearethephonecompany 

Gr8.  You’ll know you’re on the right track if you see a gray gear appear along with a progress bar on the bottom of the screen.  

No luck. The only difference is that now there is an ad for U-Verse on Demand as the receiver goes through its useless cycle of endless reboots.

This took some effort because the TV is across a basement from the gateway. Luckily I had some long ethernet and hdmi cables so that I could hook the tv to the receiver to the gateway.

Also, I went through the whole unplug/replug everything from the gateway to the DVR and WAP and receivers, again, because I hadn't really rebooted the gateway earlier. I thought that the gateway was the wall-mounted modem and not the AT&T router. Anyways, I believe that this last full cycle restart cycle is what made things change to add an ad to the cycling process, but in the end, the receiver appears to be lunchmeat.

I'll contact AT&T and get a new receiver. Thanks again for the help. 

Just to close this out: I got a replacement box. Oh well, wish I could have fixed it.

Well, it’s not an advertisement for on demand, @wearethephonecompany , it’s one of the native functions of the service. After the box finishes its initialization process, the On Demand screen is typically the first one presented to the user.  There’s some additional time taken to retrieve the recordings info from the server, but the settop box should be useable right away.  

Bummer though about needing a replacement.  It’s probably fair warning to point out anything you’re sent will be used and I bet as old as what you had before.   

The reason I had called the On-Demand splash screen an ad was because it was a change from previous behavior, where the screen just said 'Press OK to watch TV'. 

Anyways, the box they sent was different (replacement: Arris, old box: Cisco). The first time I went through the setup instructions, it would've sat on the U-Verse splash screen for as long as I let it, but after restarting the new box, things were OK.

So... all's well the ends well. 

Cheers.

@wearethephonecompany 

Sounds like a textbook hardware problem. Glad you got it working!

U-verse TV has many times given me the on demand screen when the settop box goes through a cold start.  I’d consider this normal.