I had the same problem with my 50 birds months ago, they would sleep right outside of the coop on cold nights. You see when they don’t go in the coop at night, it means they haven’t established that that is their home, they haven’t made an attachment to the coop, they haven’t established anywhere as their home as of that point, so what I did was go outside every night and give them some type of trigger to go in the coop, I put a light inside the coop on a timer when the light came on at dusk I would shoo them in the coop and leave enough food and water in there for the evening, then I have the light on a timer and had it shut off after an hour and a half later once i saw they were all settled in, after about two weeks I no longer needed to shoo them in for the night, as soon as the light came on at dusk they knew it was time to go in,it was a trigger. this doesn’t always work but certainly something you could try.