Prolapse is personal
genetics and NOT something you are doing.... as long as you aren't providing artificial light to keep production up.
Your best bet is to cull the hens who keep getting prolapse. But have you tried a vent sling to keep the prolapse in longer term? Thing is, once it happened... even just passing poo can cause it.
You MIGHT be able to get an implant that stops them from laying for a while... to let the prolapse try to stay tucked in longer for healing. But that would be pricey. My guess is that you hens who are prolapsing... would pass from egg binding if they didn't prolapse.
Sorry you face this... Prolapse is something I do cull for, as I find it VERY likely to repeat itself... inviting pecking and other possible issues.