We play in a server with about 5 players but this problem still happens when there is even just 2, we can never get mobs to spawn (server is not on peaceful) sometimes they do spawn usually only when all players are in the same area but it is quite rare to spawn, also when for example most player are in the over world and one player is in the end, 0 endermen will spawn. Thinking it has something to do with the amount of farm animals we have? Or maybe some sort of max cap of spawns allowed? Which is very annoying for when we need mob loot.