I have not experienced where all the hens all of a sudden one day laid outside all over. I have on rare occasions had one hen start laying outside the coop when she had been laying in the coop but that was in a hidden nest. I’m not sure why she did that but a month or so later one did go broody. Maybe she was looking for a hidden nest to make a clutch and hatch some chicks. But it was all of yours, not just one.
I’ll ask the silly question. Were they accidentally locked out of the coop and away from the nests? That can happen.
I don’t know what happened. Either they could not get to their regular nests because of some physical barrier or some critter or something they were afraid of was in there and they did not want to face it to lay their eggs. It would not have to be a critter. It could be something strange that they are not used to, especially if it was something moving. Was a piece of plastic flapping in a window? If none of them laid in there it would likely not be a critter because they lay at different times of the day. Even if some were frightened early by a critter, it would probably have left before the late layers were due to lay.
Did they all go on the coop to sleep as normal? If something was scaring them it might have carried over to roosting.
Do you have anyone around that likes to play practical jokes on you?
I’ll admit that one sounds strange. I don’t know what happened.