Well, to be short and exhaustive with that is a madness. But i can throw some hints. It’s not so uncommon, and it take plenty of different forms : twos seedlings from one seeds, one plant with four secondaries per node that suddenly split in twos apex (or not), a fews others variations of both and also the “celery syndrom”.
It’s hard to process at the begin but it come from the ovary of the mother (of seeds). Cannabis females are prone to produce double ovary, and all errors in between. It end with “siameses” that can take surpsing shapes. In your case, you’re in front of a “failed blueprint”. And these mutants are not specifically prone to hermaphrodism.