Mac Mail stuck in "moving messages"

I have seen many questions about this, but no clear answers. My only solution is to actually delete the IMAP account and create it fresh again. This all happens regularly and I have since been incredibly aware of attachments, what I delete, making sure I minimize forwarding and try to use reply all. I try to never drag addresses from between to:, cc: and bcc:. etc.

But there must be something that I keep doing that creates this problem. It might be that I access mail on my iPhone in addition to my Mac and that gets the synching out of whack. I just have no idea what behavior I should change.

None of the reboot, restart, etc. matters. My IMAP mail server is IONOS (formerly 1and1.com). But this error is specific to the Mac. Looking on the browser or the phone, I see nothing.

Right now it is stuck at "Moving Messages 1 of 2". Is there any way I can inspect what is going on? I do know from experience that if I continue to access mail this number will just keep climbing and be stuck and both numbers will continue to grow until I do the delete and start again.

Any ideas?