Two things come to mind. The use of a paint/primer combo. I have found this type of paint isn't as good as a dedicated paint. It is a good idea to prime your wall covering and a good dedicated primer will work better. Plus a dedicated semi-gloss paint will do much better and be more resistant to moisture.
Another thing is the color. Such a dark striking color demands the need for extra binders to hold all of the pigment. What you might be seeing is the loss of binders, exposing the pigment.
I would repaint with a good regular paint. Priming now isn't needed. There are many brands that are better; Sherwin Williams and Benjamin Moore come to mind.