Any time you add new members to a flock it cause stress and can stop laying. Once they are comfortable and the new pecking order is firmly established, they resume laying. It's also about time for their fall molt. Most hens stop laying completely while molting. Growing in all those feathers takes up a lot of protein and energy. Some hens resume laying right after they finish molting. Some hens won't start laying again until spring is on the way. That's just the way it is with mature hens.