I grew up on a farm with 200 to 300 hens use for egg production. ONE- avoid giving egg shells to your hens. IF you do, bake them first, then crumble them well. Better to feed oyster shell. TWO, make certain a varment or snake is not helping themselves. THREE, keep your nesting box padded well, &/OR make a slanted floor in the nest box so the egg can roll onto a protected area.
My aunt had heavy oil cloth nailed to the back of the nest box, and the egg rolled under it, the hen couldn't see the egg, so it was safe! I noticed that when a young hen first starts laying, her egg shells are not perfect, and appear not as complete. Those are the eggs I have seen get broken when the hen gets up, then she or any other hen that see the broken egg eat it. It can become a habit quickly between the hens to eat eggs.
Also REMEMBER, shortest days are in December, the number of hours a hens eyes see daylight determines the number of eggs produced. Thus, long summer days produces many eggs, short winter days produce fewer eggs.