chickens eating "defective" eggs

[lazy gardener]

Leaving them large keeps them in the digestive tract for a longer period of time, And feeding them in the evening puts that calcium in their tract in the evening when the egg is in transit past the shell gland. (at least that's what a recent study I read indicated.) Interesting that your flock seems to chow the shells in the evening!

 

[aart]

Tho eating thin or soft shelled egg is 'fair game',
and usually is not a gateway to egg eating,
if a frequent enough occurrence it can be come a habit for some birds,
and they may seek further opportunities in trying out the well shelled eggs.

If you have a thin shell layer(I do) it's good to gather frequently to remove the opportunity, or at least get it out of the nest and toss on the ground.

Keeping fake eggs in the nest can also help curb the formation of a bad habit.
I regularly swap fresh eggs for fakes throughout the day,
but am retired and have time for such an endeavor.