Deep, irregular cracks resembling dried mud in dry paint film.
Remove the coating by scraping and sanding. Prime and repaint using a high quality waterbased paint. Mud-cracked areas can also be repaired by sanding the surface smooth before repainting with a high quality waterbased paint. This type of paint is likely to prevent recurrence of mud cracking as it's more flexible than oil based paint. High quality paints also have higher solids content, which reduces the tendency to mud crack. They also have very good application and hiding properties, which minimize the tendency to apply too thick a coat of paint.
Source: The Paint Quality Institute