I'm betting it's hotter and/or stuffier inside the coop....
.....maybe try opening all those windows?
They are all open! 24/7 in fact. There are also open eaves the whole way around the roof. These pics were taken in the winter time. Plus the whole back of the coop is two large doors and I have them propped open a few inches as well.
I have been checking my thermometers (one inside coop and one outside coop) and it is usually about 4 to 6 degrees cooler in the coop than in the run. Go figure. I think they are just weirdos. LOL!!!