Sounds like heat stress to me. Where are you? What is the temperature? Do you have photos of the birds you can post? Egg production is secondary to keeping them hydrated and as cool as possible, though that is a sign/symptom of a heat-distressed bird.
Be sure they have PLENTY of fresh, cool water - drop a few ice cubes in the water stations if needed. Electrolyte supplements in their water will help them fight the heat as well. Also, you can use trash can lids to put little wading pools in shaded areas that they can stand in to cool down - a few ice cubes in those doesn't hurt. Fans work well to move air over the birds to help them dissipate some of the heat in and outside the coop - you can put a box fan in their run blowing about half speed to knock some heat down. You can even bring the birds into an air conditioned space of your house to cool down if you're so inclined.
We use a temperature-controlled exhaust fan in our coop, additional oscillating fans in thh coop during the first 4-5 hours the birds are up for the evening, misters in our run that we turn on during super-hot days, and we have at least five or six water stations in and out of the run (they free range the last few hours of each day).
When trying to keep the birds cool, we try to think of things that would help US cool down, then apply those solutions to our birds.
