I highly suggest buying or borrowing a trail camera, perhaps from an avid hunter to see who is getting into the run and how. There are so many possibilities. Finding out for sure what kind of predator is the problem is key to the solution. Our run is not predator proof, but the coop is and all hens get locked up at sunset. One of our neighbors was losing hens to a bobcat. (She found out by putting out a trail cam). Another lost hens to a dog. We lost rabbits to a raccoon. I think we lost a hen to a snake, (constrictor), only be ause she was in the way of the eggs.snakes don’t usually kill osmething larger than they can eat, but are capable of squeezing a hen to death if they are in conflict over eggs. Our owls, opossums and coyotes hunt primarily at night when our hens are in lockdown. I have lost two large roosters to a hawk in the daytime, but was blind in one eye. The hawk did not attempt to get into the run. They like to be able to fly in and fly out easily ir don’t risk it. Securing your hens at least temporarily so you can catch the predator on camera, will make it easier to defend against.