They could be stressed. Also my oldest 2 year olds will take long breaks in between egg laying. At 2 is When their laying starts slowing down. Or if they free range, they are laying outside the nest box in a good hiding place!
I couldn't figure out why I wasn't getting ANY brown eggs, just blue and green last couple weeks. Well, my dogs one day found a huge pile of all brown eggs and another small pile. One in our back woods and the other under the neighbors pine tree, which he has several. I have a hen that lays in a special spot in the garage too. I have about 6 brown layers and 7 blue and green layers. Soon I'll have 4 more layers(3 blue and one brown) that will start to lay. Chickens are addicting!
Good luck! I hope you figure it out. Also, they won't lay if they are not getting enough protein or food.