the warning suggests that you have a literal "INBOX" folder in your maildir, next to the "Inbox" you actually want. you should delete it after making sure there is nothing worthwhile in it.

the error is more mystifying, as this shouldn't be even possible with MapInbox. that might be a genuine bug.

however, your summary line says 4 boxes, while your pattern specifies only 3, so something is inconsistent here.