I had a couple of hens who were laying and both sisters of the same hatch and parents. I found one day that both would slightly prolapse when laying eggs. I tried pushing them back inside, but with their straining and struggling when handled, they just coming back out. When I finally left them alone, they were fine and just went back inside. They seemed to both have an overly relaxed vent, and though it would come out a bit with laying eggs, it always went back inside on it’s own.