The fact that it peels off says to me it's been resprayed at some point and not very well. Maybe an incorrect primer. Even if there is a stone chip a jet wash won't make it peel off if it's good paint. I had some extra plasticiser put in some arches I had on an old car and you could practically bend them in half and the paint stuck fast. If the prep is good there shouldn't be any issue and I'm sure the factory doesn't do it incorrectly, so my money would say they have been sprayed at some point. When I machine polish customers cars you have to go easy on bumpers as the plastic/paint heats up a lot quicker than on metal and can bubble. A good job shouldn't have any issues with a pressure washer and anything above point blank is ok. You can stand right in front of one after a few inches and it's just mist.unfortunately it's going to need a respray to sort that, and be prepped correctly.