Chunks disapear when you fly above them

Put the summary of the bug you're having here

What I expected to happen was...:
When a chunk generates I expected it to stay generated.

What actually happened was...:
The chunks disappear for 10 seconds

Steps to Reproduce:
1. Fly above a world to generate more chunks
2. sometimes a few generated chunks will disappear like in the top picture.
3. and other times a whole group of generated chunks will disappear for 2 to 10 seconds like in the bottom picture