I have a broody hen sitting on 3 eggs about to hatch right now. She had another egg but it was supposed to hatch 3 days before the others. So I brought it inside to the incubator so she wouldn't abandon the other eggs when it hatched. Well I candled it on day 17 and everything looked good. It was taking up most of the egg and looked normal so I left it to hatch. It never did. I left it in there for a couple extra days and still nothing.

I thought maybe the incubator was warmer than the broody had been keeping the egg.

Any ideas why it developed all of the way and then didn't hatch???

I've had this happen once before, and I'd like to know what could cause it!