I have oyster shell free choice, but that doesn't mean they are eating it. My black sex link hen has been a great layer with an egg most every day. She started with soft shelled eggs after i switched. The other hen, an easter egger is still in her first year of laying and just layed a soft shelled egg today and I've never had any problems with her eggs. She lays most every day also. The only thing that changed is their feed. They free range a couple times a week as usual and I offer them a little BOSS in the evening. So if the switch in feed isn't causing the soft shelled eggs than what is?