I've all but given up. It's gone beyond the sign in problem. Now I jjust get a "server error" page every time I attempt to get past my profile after signing in. I was able to sign in this time (after getting an error) by signing out, signing in with my wife's account, signing out of that, and signing in again with my account.
I have modern hardware, Running up to date Windows 10, and have used up-to-date copies of Chrome, Firefox, and Edge. I've also had the same problem on my wife's similar machine, the media server, and my work laptop. All up to date with correct javascript, etc.