I just added an auto door since I finally have power at my coop. I used a plastic cutting board for the door an be it slips behind the ledge so it can't be easily pried open. The motor is on a regular house timer and I've adjusted it over the past few nights to ensure its closing at the optimal...
It may be too dark in the coop. If they are staying out later and you don't have a lot of windows they may not be able to see well when trying to go roost.