Backyard Fowl Keepers

It might just be a phase. Sometimes chickens do weird things for no obvious reason and then snap out of it a few weeks later. I'd keep guiding them inside until they relearn the habit.

Cold air might actually be more comfortable for them than a sealed-up coop, especially if ventilation isn't great. Maybe check your airflow balance inside,too stuffy could be just as bad as too drafty.

Something may have spooked them in the coop,predators, drafts, or even a sudden noise at night. Have you checked for signs of mice or other small intruders?