Put the summary of the bug you're having here

What I expected to happen was...:
Describe what you thought should happen here
The chunks should load up quickly because I have a fast computer.
What actually happened was...:
Describe what happened here
The chunks failed to generate. There was nothing but is sky in most cases.
Steps to Reproduce:
1. Load up my Minecraft world.
2. The chunks don't generate
3. The game crashes when I try to exit to them main menu. I have to close the game down completely to stop the bug!