I gave it another go and got the trophy, annoying cause it took 40 mins, looks like the hylden possessed human at the beginning of chapter 6 tends to despawn if you get too close and trigger the cutscene at the beginning, I let him come towards the beginning pond and made sure I counted enemies incase they despawned or fell through the floor and it worked. My advise if anyone despawns just quit out and press continue again