Any ideas as to why this has happened?
Have you checked the nests for pests?
Dimensions and pics of your coop, inside and out, would help here.
How many birds do you have?
Can I get them to start laying in the coop again?
Free range birds sometimes need to be 'trained'(or re-trained) to lay in the coop nests, especially new layers. Leaving them locked in the coop for a week or so can help 'home' them to lay in the coop nests. Fake eggs/golf balls(do not use real eggs) in the nests can help 'show' them were to lay. They can be confined to coop and maybe run 24/7 for a few days to a week, provided you have adequate space and ventilation, or confine them at least until mid to late afternoon. You help them create a new habit and they will usually stick with it. ..at least for a good while, then repeat as necessary.
Oh, and...
Welcome to BYC! @JRherrin
Where in this world are you located?
Climate, and time of year, is almost always a factor.
Please add your general geographical location to your profile.
It's easy to do, and then it's always there!