Spraying to thick, especially rattle can laquer paint will do it. So important to do a super thin fast coat first. Also, was it cold out?
I NEVER wash the bodys I paint. I pull them straight from package and liquid mask them. I have never had one flake. On that note, I use fascolor and have noticed that waterbased seem to be better at flexing with the body than laquer. Just my experience of course.