That's what I suspected. If I'm not mistaken you only have a two-hour window to recoat over the primer. After that you have to wait 48 hours before recoating. I used Rustoleum on my wheels and had the same problem you did. First coat looked like glass. I came back the next day and tried to recoat and the painted fubared almost instantly, crackling everywhere. It's unfortunate that you had to learn the hard way like I did. The only thing you did wrong was use Rustoleum. But I didn't sandblast, I just sanded everything back down smooth and started over. It was a PITA and I will never, repeat never, use Rustoleum again on anything. Good luck.