I make no assumptions 
I’ve seen people have issues connecting to the router and then a repeater which run upstream to the same router. Another issue could be a firmware update from the provider and if you are using two separate networks but both on say Comcast you could encounter this.
Correct, this would be a 3rd network that is completely separate.
That’s why I suggesting going someplace and trying the guest wireless there.
The answer turned out to be…
VPN!
Two were struggling to control, only one of which was readily known to me. Killed both, all is right with the world.
I didn’t actually check for it, I was just watching the screen and I noticed out of the corner of my eye some jumping at the bottom when the on/off was happening…
That’s the first mention (other than an unanswered question by @zbuzz earlier) of a VPN. That might have been good to know upfront, since it changes the troubleshooting process quite a bit.
But you eventually figured it out, which is good.
If I had thought to mention it, I would have figured it out. I am very new to using VPN, and one of the ones running I didn’t have any recollection of installing at all…yeeps.