Once there are enough eggs + chickens in place they seem to stop making eggs. If you have too many chickens they simply refuse. Just like if you have too many boars and such they refuse to breed. I have a pretty big hen house, split them in 11 pairs and they could only lay 8 eggs, so i guess 30 is the max in an x area. I reduced them to 8 pairs, seems to work better.

Also, just collect like 100 eggs and hatch them all at once, do know that chickens climb one another so it's going to be a hellhouse at some point.