How old are they, how many, and what is the laying pattern (how many for how many days)? Do they free range?
There are lots of different things that could be going on. Can't cover them all. It may be something normal, could be a reflection of the heat or other stress, like running out of water. They may be hiding a nest. Maybe something is getting the eggs. It's hard to get very specific without more knowledge. Even then it's often a guessing game.