Thread:HubToo/@comment-25359794-20151017123609/@comment-25612015-20151017145156

I also read that in the Custom NPCs FAQ:

My mods work great on singleplayer, but not on my server / Npcs wont spawn/ Npcs are invisible. Short awnser: The mods on your client and server need to be exactly the same. Long answer: To prevent entity id conflicts there is a function called getUniqueEntityId which gets a unique entity id for my npcs. What happens if your client has more mods with entities is that the entity ids arent synced on server and client, because the other entity took the entity id one of my npcs should have gotten. So don’t use mods that add entities on your client that the server doesnt have. It can also be that if you are using things like worldguard that its preventing them from spawning.