Probably a result of softer shells caused by inadequate nutrition. There are a few very essential minerals that are required for strong shells. Unfortunately most people only think of calcium as being important for strong shells. But there are 5 or 6 that are critical, not only the correct levels, but the rations between each other. Also, if the diet was deficient in these minerals, it may have caused the chicken to become a little nervous and that may cause them to eat their shells.
We recommend feeding Purina Mills® Layena ®SunFresh® Recipe® to avoid this problem. Layena® is formulated with added Vitamin D3, phosphorous and other essential minerals for strong, hard shells.
Now here is the problem, when you switch from your current feed to Layena®, the birds have already developed this habit and may continue to try and break the eggs. They like the taste of the eggs and will purposely try and break them. So what you need to do is to collect the eggs several times a day for a couple of weeks so that no eggs get broken. This should break (no pun intended) the habit and allow you to enjoy your farm, fresh eggs.