We have 2 Isla Browns. One of them seems to be 'holding' onto her eggs. We do not get an egg one day, then the next we get one egg, layed anywhere in the coop that is discoloured and in less than an hour there is one in the nesting box that is not quite formed with a soft shell. This is happening several times a week now. She use to be very good. The other chicken is laying fine. They have shell grit and layer pellets. Any ideas?