Mobs both passive and enemy are not spawning in loaded chunks when below Y= 29. I was trying to map out Slime chunks when the new update was pushed today so I had command blocks running detecting entities and killing them. When Y = 30 or above mobs started to spawn slowly. I have created around a 250 x 250 dark flat room and as i approach it in the center mobs gradually quit spawning down to not a single spawn with the command block confirming it. The spawning area is Y= 6 - 15 completely clear. No mobs are spawning in the caves above that level either also confirmed by the entity checks. Playing on hard difficulty also effecting superflat worlds. No mobs are on the ground when loaded in. Even on hard difficulties mobs will not show up until Y > 29. Including passive. Time was set to night.