I built a high efficiency mob farm as shown in this video (https://www.youtube.com/watch?v=YA2siTV5s4Q) that works perfectly in a singleplayer world and in vanilla 1.8.1 minecraft servers, but on realms no mobs spawn in the farm. The light level throughout the entire farm is 0 and no other players are on to split the mob cap. I am the required distance of 24 blocks away from the farm and no other mobs are spawning underground because of my position of y160. From what I have found on google, it is because there is a bug that mobs won't spawn properly in render distances under 10. Thank you for taking your time to look over this bug.