The bug

It looks like the world generation can spawn too many monsters at the same place.

Note: MC-4061 is marked as related since Marcono1234 had one chunk error while trying to reproduce this bug, however that time no monsters spawned.

How to reproduce

Outdated, though this issue might still occur

1. Ensure your render distance is set to at least 9
2. Create a default world with the following seed

   8627439086671208170
   

3. Teleport near the position

   /tp 920 70 -1736
   

4. Wait some time, maybe about 10 seconds
5. Switch to Spectator mode

   /gamemode spectator
   

6. Teleport to the exact position

   /tp 908 27 -1774 180 50