It can crack yes.
First question: Is the ink cracking on all the shirts? Is your dryer very consistent with it's heat output? Is there anyway that the heat could have dipped low enough to not fully cure the puff ink for a few shirts here and there? Are ALL the customers shirts cracking?
Second question: Is it possible that you added a bit to much puff additive to the fluorescent ink? By doing so you reduce even more it's stretch ability. That coupled with the possibility of the first question could be your culprit.
There are always several things that can go wrong when mixing and curing puff inks.
What mesh count? One pass? p/f/p? Was it printed on top of another ink or by itself?
As additional info: If you really over add puff to an ink you will see the print crumble when you brush across it. It's really weird