The problem first appeared after the July 1st update. I tried all the steps suggested here to no avail.
Then I found a homebrew solution: After reinstalling, I chose “I’m new” and then logged in from inside the tutorial. Once I was logged in once, the problem was fixed, strongly suggesting to me the problem is with the log in server.
Sadly however, for no particular reason, I’m stuck again, and my “fix” doesn’t work this time. Any help would be much appreciated (but please no “Try the steps shown in Pinned Blue Post X”, I’ve tried those, several times.)