You shouldn't worry they have off days like we do, mine are a couple of year old and every so often we get soft eggs, no shell or very strange looking shaped eggs. It usually rights itself after a few days. So long as they are feeding well have access to grit and oyster shell they will be OK. I also give mine seaweed, garlic flakes, poultry spice and cod liver oil a few times a week, but whether its absolutely necessary I don't know, probably overdoing it, but it makes me feel better if not the chickens lol alison