You should have some oyster shell available to them so they can eat it if they need more calcium. I have a little bin in the run with that available plus I also give them crushed up egg shells.
It is filled with hay. I just refilled it extra today to make sure that wasn’t the case. Maybe that will help!
Is the shell there thinner?
When some of my hens got into this habit, first of all, I made sure to get any newly laid eggs quickly out of the nest boxes. Then I replaced them with wooden eggs. The hens who were responsible would give up this behavior after a few days of pecking wooden eggs and getting no results except perhaps a sore beak! It worked beautifully.
Sounds like you hens don't have enough shell grit in their diet (calcium deficiency). You can buy commercial crushed seashells, but don't add it directly to their feed. Put the grit in a separate container so the hens can get some when they need to (like now). There are also nesting cages that let the egg roll down a ramp away from the hen (like they have for battery hens). I also boil used eggshells and crush them. I add the crushed eggshells to their scraps from the kitchen. You'll know they need calcium because they will pick out the pieces of eggshell even before they eat the food scraps! P.S. remove eggs from the nesting box as soon as they are laid (if possible). When you hear your hen "buck-buck-buck-bagaark"-ing, there's an egg in the box! You need to get to it before the egg-breaker!
I've been working on this problem for a while now. I have filled eggs with mustard, that was interesting LOL. The egg was still broken, maybe even eaten some and, like she was mad, tossed it all over the place. Still eggs were missing so I added food dye to the mustard,to find the actor, I had blue all over my hands. One perfect one I was admiring and proceeded to drop it on my kitchen floor... none of the next ones came out as good. I have two coops so I needed eggs in each coop. I have curtains on the boxes already, well strips of fabric stapled to the entrance, but painting black might be the next thing I try.
