If this was indoors and a photosenseitive plant, climb inside your tent, zip it up and look for light leaks. (The last time I did this, I was surprised at how I overlooked a powerstrip in the tent with an illuminated on/off rocker switch.). If you don't see much light leaking, what were the temperatures during flower?
It must have something to do with stress. If you used feminized seeds, they're more susceptible to herming (more sensitive to stress).
Honestly, I like it when I get some seeds that way. I like the free seeds. And, honestly, I like growing bag seed better than designer genetics. I feel like all the designer "breeding" is wrecking the genetics. I think bag seed brings back some hardier latent genetics.