I have a vanilla survival server for me and my two friends (bought through MCProHosting) and I made a mob farm like most tutorials on youtube show. Simple 20x20 farm in the sky with 4 water stream (2 blocks wide) pushing mobs into a 2x2 hole that is roughly 28 blocks deep. At the bottom are hoppers which are attached to a chest. There is absolutely no light in farm, and the server is set to difficulty 3 (hard). Howcome mobs aren't spawning? Is it something configurable in the server.properties or is this a unique problem?