The first thing I saw was China.... it is certain why there is a problem.
Aluminum sometimes needs a bit of extra care to coat properly, especially when smooth. It sounds like they parts were not properly cleaned.
I remember doing refrigerator parts years ago and I think it was like 1000 hours salt test. I may be wrong, it has been a while. But on the parts that did not pass, you could see speckles of rust starting to show through. Not sure how well it would work for aluminum.
Contrary to what was stated, when cleaned and applied correctly, powder coating is super durable and does not flake from a damaged spot. At least particularly on steel. Assume you knock a chip off, it should not flake from that spot over time if it was done right.
Where I was, we used an alkaline bath to cut any oil, through a rinse, into an iron phosphatizer, rinse, and though a drying oven. The iron phosphatizer would etch the surface of steel and leave it ideal to accept the coating. Curing the coating is also quite critical for durability. I had some strips of light guage steel that I abuse tested for the fun or it. Beat the piss out of one with a hammer and was only a few cracks where it was bulging through. i doubled one over and maybe one crack, no chips or flakes. Only when I squeezed the bend tight in a vise did a chip or 2 come off and a few more cracks. But around the chips and cracks, the coating was still adhering to the steel.
Perhaps the parts in your question were not well cleaned or possibly not dry. That will cause blistering, be it visible or not. Also, we had some issues with some sandblasted parts. It was claimed by someone that sandblasting would lay over high spots and trap air or dirt, causing blistering.
Any oil at all will cause it to not adhere properly, and likely leave pinholes where it baked out in the oven. Even oil from using bare hands. clean gloves should always be used when handling before coating.
