I am receiving regular Thunderbird notifications of errors for a Yahoo mail account

One possibility is a corrupt index file. Try rightclicking the folder and click repair

One possibility is a corrupt index file. Try rightclicking the folder and click repair

I have tried this even though the folders had been recreated when I deleted and re-added the account. The issue is still occurring.

I have regularly received these same errors for months but have not been able to make them stop. There have been a few other reports of it here, too. They are annoying but not fatal, that is, mail fetching and sending happens anyway. This only happens with one of my two Yahoo accounts, and happens on multiple computers. I've gone so far as to remove and re-add that account to Thunderbird with no positive effect. I suspect it's a Yahoo issue, not a Thunderbird one

I just found one report suggesting that the "UID FETCH completed" messages could be related to a corrupt index on the SERVER side. I don't have time now, but I think I will move all messages out of the Inbox using webmail in hopes that will set the folder right. I'll report back later with the result.

The UID FETCH message is related to a failure to retrieve an IMAP message. Since you have already addressed possibilities that lie within thunderbird files, i agree that the problem may be a server-side problem with Yahoo. Or related to antivirus or firewall