I read somewhere that maybe the panels weren’t cured or dried enough during manufacture, and maybe should be left to cure longer… but I don’t think that’s it at all. You could probably bake these panels for months and still have this issue later.
I suspect this is caused by water inside the door, even if only a tiny bit, then the door absorbs it into it’s unpainted surfaces… after warm/cold day fluctuations the water evaporates and tries to escape wherever it can in a gas form. Causing the bubbling on the painted side if it can’t escape any other way. I wonder if leaving the windows rolled down on a hot day would help the water evaporate out
These are basically fiberglass/plastic panels, correct? Maybe not enough epoxy in the door panels at the time of manufacture created a porous panel, or maybe certain panels have micro cracks or minor damage from handling that allows water to soak in, then weep out later. Water always looks for a weak point and will find its way in. It is insidious, then progressively gets worse if you don’t notice the water damage right away.