I’ve never heard of chickens eating fertilized and growing chicks in eggs.
If it truly is your hen doing it, I would get that hen out of your flock, or at least find ways to stop her, as egg eating is both addictive and contagious to other members of the flock if not from a health reason.
But I also feel you shouldn’t rule out a predator, even if you’ve never had one.
Are you finding eggshells? Chick remains?
I did some quick research, there are some ways you can try and stop a hen from eating eggs. The most notable one was blowing out an egg (making a small hole to dump contents of egg) and fill it with mustard, because apparently chickens hate mustard! When she breaks open the egg, she will get a helping of the tangy yellow stuff instead of the yolky good stuff.
Do some studying yourself, as some of these solutions are keeper-specific, such as adding nest boxes or adding excitement for your hens every-day.
As for my personal solution: I don’t give my hens the chance. I collect daily and incubate/hatch my own eggs.
