Thunderbird no longer updating my iCloud mailbox

I've been using Thunderbird for my iCloud mail for years. I have two factor authentciation enabled and use an app specific password generated from my AppleID accont. This has always worked fine. Today I noticed that my inbox had not updated the past 24 hours, and the one new message in my inbox always remains new, even after clicking on it. I can see new messages on my iPhone that I'm not seeing in Thunderbird.

I restarted Thunderbird, but that didn't help. I then deleted my app specific password and restarted Thunderbird again. That resulted in the expected prompt to enter a password. I did that with a newly generated app specific password. No errors, but still no inbox update. I then tried sending an email to a different account (not icloud). Once again got the expected prompt for (smtp) password. I entered it. No errors and the message was sent and delivered.

I tried "Repair Folder" on the INBOX. After doing a bit a work, it seemed to get stuck with the message "Downloading Message headers 1 of 21 in INBOX" on the bottom of the screen (there are probably about 60 messages in INBOX). Then after a while it updated a different account (probably automated periodic checking for new mail), so that ended up erasing the message.

I'm using the Thunderbird 78.10.0, which is the latest and looks like it was installed 6 days ago. Any suggestions?

[Update: I just noticed my wife's account is working fine.]