If I'm reading things right, you say that the fish eye happens in the same spot every time. That means there is contaminate on that surface. I to have had that problem, really pics a guy off when you do a beautiful job, come back an hour later and it still looks ok, but now you have a little pin hole, 2 hours later... BAM it looks like doggy doo. The best I can explain is to take some MEK and put it over the affected area, let it dry good and cross your fingers and paint again.