Ok, firstly thanks for all the replies.

We got the door open, and the problem was my fault, dammit. When I reinstalled the locking mechanism in the new door shell, I accidentally reassembled the link rod from the external handle incorrectly. I had installed the rod on the wrong side of the lock slot, which caused the rod connector block to be trapped between the lock mechanism and the door frame. We removed the lock, assembled it correctly, reinstalled and the door opened and shut perfectly.

Thanks again.