Hi mate thats microblistering, obviously the panals been painted before, and its moisture in the layers of paint/ Can happen for a number of reasons, but more commonly when painters don't use a decent water trap on their compressor, you wouldn't notice it until you get a cold batch of weather or loads of rain and the moisture expands, greating small blisters and in turn lack of adhesion/ i.e paint flaking off.
Strip Respray the relevant panals and possibly blend into the adjacent panal is the only option.