So this is what happened to me twice. Notification of a new message pops up, I click on it and after reading the message tap on the right corner menu (three dots) and Move the message to xyz folder.
Everything seems fine but if I open the webmail client I can still see it in the Inbox. Somehow the messsage was copied by the app but just locally. In fact, the message I now have on xyz folder cannot be moved elsewhere because is not synchronized with the server.
Something odd is happening with such a basic feature that I never recall to behave like this.
I’m running K9 Mail release 5.734 on Android 11 ROM with an IMAP account.