Use a good quality primer like Tamiya primers, you wont have issues like this, in my experience, its far better that Duplicolor primers.
A real rule of thumb to try and follow is to stay with the same brands when it comes to painting, since you used Duplicolor primer, you should then use Duplicolor paint and then top it off with Duplicolor clear , that ensures 100% compatibly and issues like the cracking will not happen. The other real rule of thumb is to not mix and match paint types, there certain paint types you can and can not mix. When you air brush, you are able to kind of break these rules some to a degree and not have issues, but rattle cans, its a bit different.
I everything I just said all has exceptions to it so keep that in mind as well.
Put that body in the purple pond AKA Super Clean and it will be as good as new and ready for a fresh coat of Tamiya primer.