[MC-155289] Mob spawning rate in the Overworld is reduced

Notice

If you experience this on 1.14.4, please make a debug dump of your world by running the command:

/debug report

Then attach to this ticket the zip file you'll find in the debug folder of your Minecraft directory. If you don't have op permission, either ask your server admin to perform the dump, or if you are on singleplayer, open your world to LAN with cheats on.

Workaround

In previous 1.14.x release mobs could aggregate in non-ticking chunks (due to ~~MC-151772~~). For example, here's how distribution of entities looks like in attached report:

Unfortunately, those mobs need to be killed before normal spawning can be restored.

Please note that using '/kill' command will not remove those entities until player gets close enough to chunk to tick.

I guess on singleplayer setting render range to max and then slowly walking away is option for despawning hostiles. Though it won't do anything with bats.

– [Mojang] Bartosz Bok in this comment and this comment

When entering a world that was generated in version 1.14.2 of minecraft with the new version (1.14.3), the amount of mobs that are spawned in the world is reduced a lot, being more difficult to find mobs.