For the 3rd day in a row I've found a soft shelled egg under the roost. Unfortunately my camera was set to record 12sec intervals so I can't see which of my six 8 month olds are laying them. They have all been laying for about 2 months now with no issue until recent. Nice strong shelled eggs up until now. They also have had free-choice oyster shell readily available. What could be going on? Should I be concerned about illness?