Well, once the habit starts. Ots hard to stop. It likely got started because an egg accidentally broke, maybe one of your thin shelled ones. And someone found out it tastes good. Then that bad actor actively will break eggs on purpose for the tasty treet inside.
Darkened Nest boxes help because if they cant see it, they cant eat it
I cured a feather picker once with pinless peepers. She wore the glasses for 3 weeks, and forgot about it after they came off. These may work for egg eating also, but the challenge is to figure out who is doing it first.
I think it's natural for older hen to produce thinner shells as they age. Maybe others will have tips to get more calcium into your older hens system.
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Good Luck!