World degenerates, chunks "unload", crashes.

Put the summary of the bug you're having here

What I expected to happen was...:
that the world would continue to generate and load as I walked around.

What actually happened was...:
the world disappeared. the chunks unloaded and I was walking in a light blue abyss. I tried breaking blocks to force chunk updates but it did nothing.

Steps to Reproduce:
1.Just walk around for a while. It happens when you get far away from the place you start when the game begins.
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