To reproduce the below crash pregenerate a radius of 100 chunks or so and then fly around the pregenerated area, I have reproduced this issue 3 times this way:

https://gist.githubusercontent.com/MCPitman/f3171980f4740af3f5f8714e1f2907ce/raw/eab5870d0e0616b409f008d1fde5d624dfb4d663/OTG%2520v8.3%2520bo4%2520crash

Thanks, should be solved for v8.3_r4