In recent months, Thunderbird has been showing failures when marking messages read or deleting inbox messages in a Zoho IMAP account. At first, it happened sporadically, and now it occurs almost every time.
When I try to mark a message read, it reverts to unread a second or two later. If I keep doing so, it will eventually stay read after several attempts - sometimes 2-3, sometimes it takes up to 20, and today I couldn't mark a message read even after 50 attempts.
When I try to delete an incoming message, it reappears in the inbox - sometimes in a few seconds, sometimes much later. However, when I try to delete it again, Thunderbird sometimes (but not always) reports "UID move failed", and if I switch view to another folder and then go back to inbox, it may (or may not) be gone.
All this looks like an improperly handled race condition in IMAP. Notably, it happens in Thunderbird on Windows, but never in K-9 Mail on Android, so maybe it can be remedied by some Thunderbird settings, but which ones?

UPDATE: Now it happens in K-9, too :-( So the problem is definitely on Zoho's side.