"Authentication Required" password request loop on Ubuntu 20.04

I have a dual-boot laptop (Surface Book 1) that can run both Windows and Ubuntu. Two days ago, on Saturday, everything was working fine. Now, only Windows can connect. On Ubuntu, it can see the wifi, and will attempt to connect, but it bounces me back to the "Authentication Required" page where I reenter the password.

I've tried restarting the router, turning my computer completely off and on, and verifying (many times) that I'm using the correct password. Among many other things! Some 5 hours of work has gone into this before I posted this question.

What can I do to resolve this?

Edit: I should mention. This appears to be a problem specifically between Ubuntu and my Xfinity wifi. When I turn my phone into a hot-spot, it connects just fine.