It may be too hot, they could be taking a break, or if they are ill with a crop problem, coccidiosis, or a reproductive problem, those things can affect them. Are any having diarrhea or not eating well? When you feel for a stuck egg, you just insert one finger into the vent up to 2 inches. If there is no egg, it should only feel soft. Some hens with reproductive problems can lay a shell-less egg which may be hard on them. Another thing to look for is that they may be laying in places other than the nest box. Make sure that you are feeding layer feed with some crushed oyster shell available for them to take if needed. If any are having frequent runny poops, you might get some checked for coccidiosis and worms, or start them on Corid for 5 days, and then worm them.