By broody box I am referring to a separate place with a nesting area and a section which allows your broody to leave the nest daily to eat, drink and dedicate.
I built broody hutches for this purpose that resemble rabbit hutches.
If you move your broody to a new spot, do it after dark. It will...
Best to remove your broody to a broody box where the other hens can not access her nest and do this to her. Chilling the eggs will likely kill reuin the hatch.
So when you found her in a different nest box and the hatching eggs in another, was there by chance a fresh laid egg in with them?
Sometimes a bully hen will intimidate a broody from "the favorite nest" to lay her
Daily egg, and the broody moves to another place.