house and wall movement that has caused this to happen. The walls might slightly move a bit enough to crumple or wave the tape. This happens allot, a great way to fix this is to install crown molding or even molding that is not crown. This will hide the situation and make the room look very nice.
To remedy this without molding, you will need to remove the tape, and install nylon mesh tape, which will allow more movement than paper tape. You could try to float over this, but this is not a cure at all, only a bandaid.