Do you have enough nesting material(straw or shavings) in the nests? Are your nests out of the way of normal chicken traffic?
I use to get quite a few eggs like that from my Dorking hens while they were in quarantine. The quarantine pen didn't have good nests with lots of cushion, so the hens were accidentally stepping on their eggs.
Make sure your nests have a lot of bedding, more cushioned the better. Also make sure your hens have access to oyster shell, that way the egg shells are harder.
-Kim