Interesting Question Pal.. I'm sure there'll be a lot of answers on this 1.
Mainly, it is just bad luck from what I've read. But they can be brought on by stress. But, if they are brought on by stress alone. Most likely, it has a natural high chance of hermies pal.
Most will say avoid this and that. But, generally I think if a pheno hermies it might be brought on my stress but it has hemie traits in said pheno. That's my take on it anyways. I havent had 1 yet, (touch bud) but I am coming into pre flower on 7 fems, so, chances are maybe 1-10 or thereabouts 1 might hermie.. and if so, 80% of the time that plant will just hermie once, unless its stressed that'll possibly bring out more. But again, just conjecture. But as I said. If you get a hemie don't throw the whole plant away. Try save her as you might get just 1, and by cutting it off. You can save the plant. But if she herms at 2-3 points during the flip. Then rid yourself of her. But again. It's rare.
Good luck.