Minecraft Forums

Hi, I've been running a vanilla server for me and my friends and everything's been working fine, but the last few days I was trying to build a Zombie Pigman farm above the nether but no mobs are spawning anywhere above the nether. I took the world folder and put it in single player and they started spawning, but when it's in multiplayer, they don't spawn above the nether. Does anyone know how to resolve this issue???