I just can't my finger on it quite yet....

Bathroom Ceiling. It's just the perimeter of the ceiling about 1/4 + 1/16" or so the paint is loosening from the ceiling. In a couple of places, it has come off, in the remainder it just looks suspect. Taking a taping knife to it, but the paint does not come loose...but I know it's somewhat loose. And it's only the edges....

I plan to just take a sander, sand it with 120 grit ....mud blend if it's bad and then prime/paint.

Has anyone come across such a issue. I don't think it's a moisture issue in the bathroom....but I can't think of anything else that would be causing this...