Minecraft wiki entry for Old, associated text: Unlocking the last tier of cartographer villagers caused the game to stop ticking.
If the player obtained an ocean explorer map or a treasure map from commands, any explored areas outside the world border were completely black. If the player attempted to get a woodland explorer map, the game stopped ticking for about 100 seconds, and an error message was eventually given.
Feeding a dolphin caused it to try to swim outside the world border.