Normally you can't move or delete system folders like Inbox or Sent in Thunderbird. How and where did you move those folders Inbox and Sent? Did this happen in a POP or in an IMAP account?

After Thunderbird updated to version 140, all my many folders were out of order including inbox, sent and Trash which ended up a long way down the list of folders. I dragged and dropped Inbox and Sent close to the top, restarted and yep all the inbox emails were gone. But later on I noticed that the old inbox was also there with the emails. So I had two inboxes showing in Thunderbird in the same account. I tried to drag the messages from the old Inbox to the new Inbox but they also disappeared. I think it is Imap.

I'm not sure I want to open Thunderbird again until 140 is fixed. Not sure what to do, so I've installed another email client in the meantime. It's a shame, because I've been using Thunderbird for over 15 years.