guineas unless raised in a coop and kept in a pen don't typically lay or set in a coop. All the guineas around here (neighbors) lay out in the woods or in the flower beds at best.
Best suggestion I got OP - give some livetraps, bait with eggs -crack one too to lure it even better. livetrap you dont have to sit up and wait. (that who a watched pot never boils applies here
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Then next time have you a 5X5X3 or so sized hardware cloth run box made and when you have a guinea who is setting and you find the nest, put the box run on top of her and the nest at night.
Try setting your guinea eggs under broody hens as well. You said you have 2 setting hens? If the hens aren't bother - stick the remaining eggs under a hen in the coop and stick the chicken eggs in the bator. Just make sure you check every morning that the eggs are undisturbed.
You may want to next year think about penning up your guineas in laying season and not giving them a choice at laying in a secure area.
Just a secure run with a covered side. or just collect eggs and incubate for now on.
Predators are always going to come, possums, racoons, foxes, skunks, snakes, etc all eat eggs.
also my neighbor has had issues with the male guineas breaking and eating the eggs under the hen to get her off the nest, and then killing babies after they hatch. so you will have to watch for that.