Same poor performance on my 5900x 12 core. Game barely uses more than 2-4 cores at max, and whenever there's a blood moon with 15+ zombies, framerate tanks from around 60-70 fps (cpu utilization limit) down to unplayable 15 fps with sub 50% gpu usage on my 2080.
Considering the game is 8 years old by now since it "released", it's performance is still dog@%$#e on the cpu part of things.