This ticket updates the mob spawning issue in 1.14, previously tracked in MC-139338 and caused by MC-144610. The same problem still persists but now under other circumstances. Now mobs stop spawning over time and it seems to be affected by the render distance. Further tests show that this issue occurs outside of spawn chunks if your render distance is less than 11.

Steps to reproduce:

1. Create a new superflat world in creative without generated structures, not in peacefull, render distance of 12.
2. Give yourself a command block (/give @s command_block)
3. Place it within spawn chunks, and make it so it will repetitively kill every mob but the player (repeat mode, always active, command is /kill @e[type=!player])
4. Set the midnight time (/time set midnight) and teleport anywhere away from the spawn chunks.
5. Notice how the mobs regularly spawn around you (by reading the command blocks output)
6. Now set up your render distance to 8. Notice how the mobs will stop spawning (ignore the chunks not rendering btw, it is tracked in MC-147532 and it does not affect mobs spawning)
7. Set your distance back to a value higher than 10. Notice how the mobs start spawning again.

Video: 2019-04-06 12-55-21.mp4

It is possibly related to MC-2536, but the issue is specific to 1.14, and this happens in singleplayer mode as well.