It isn't 'normal' but can happen from time to time. Out of several batches of fry I Got 3 defective like yours. The first is still alive the seconds back got more indented and eventually got stuck on filter...I saved her but she disappeared days later, a recent fry was kinked bending its side not its back and I'm pretty sure she got eaten when I let the babies into the young adult tank.
These fish are quite inbred to acheive coloring. Also, having a large batch may increase this chance. Water perameters should also be checked as a cause can be from poor water quality.
My water stats have been great. And yet I've still produced 3 kinked fry. All of which one is alive. Males won't pay attention to it if its a female and it really shouldn't be picked on by other males if its a male. My one surviving one is a male and the other males pay him no mind.