Problems with XB3 in bridge mode on NOW Internet

I really want NOW Internet to work for me. I've just apparently downed the second XB3 that I've had. What happens is that I configure them for "bridge mode" so that I can use my router. That works nicely, but if anything happens, my router no longer gets internet and I can't get the XB3's back into working bridge mode. The first time around, Xfinity replaced our underground line to the pole due to noise. That somehow caused me to lose internet to my router. Note that I did verify that the new line is good by checking to be sure that the XB3 was working in router mode, which it was.

I tried the usual things  one does to get that one working again, rebooting it and and my router, letting the XB3 "rest" for about 5 minutes with power disconnected and then powering up both the XB3 and the router again. When none of that worked, I factory reset the XB3 using the "reset button", holding it in for about 30 seconds. Then reconfigured it into bridge mode, and powered it down after it came back up. I again brought up both the XB3 and the router, and no dice, the router wasn't happy, no internet. However, the router has been working all along with my "other" internet, the one that costs more that I hope to stop using. I tried a few repetitions of this, factory resets and reconfiguring, and powering up the XB3 and my router, nope

Same story with the second XB3, this time the internet to my router was interrupted by Xfinity telling me to activate the XB3. I had made the major mistake of bringing the XB3 up, into bridge mode, and getting my internet going on my router before I activated the XB3. Not sure why that worked, in retrospect, but it did, and worked well. So I scanned the code on the XB3, and Xfinity activated the XB3 (they said). After that was finished the XB3 rebooted, and voila, no internet to my router. So I went through the whole song and dance again with factory resets, resting, reboots, a few times, no luck again. This time around I even tried the factory reset that's under "Troubleshooting" in the web admin interface for the XB3, and again, of course, the XB3 didn't work right after that, either.

Are these XB3's re-usable? Or are you supposed to throw them out after a single use? I've never encountered such fragile hardware before. How in the world do you get them to work a subsequent time if doing all the usual things that one does with this sort of hardware don't help. Is there a secret that I'm not in on? I'm going to get a new XB3 on Monday, hopefully it won't be another single-use piece of hardware. If it is, I guess that NOW Internet isn't for me, and I'll go back to AT&T fiber that I've had no trouble with in the last 6 years. Been using my own router for years and years, long before being on AT&T fiber as well...I'm what you'd call "experienced" *smile*.

Thanks.