Voxel Generation issue and crash

UPDATED moved to 4.10 Same result

So im following this Twitch series learning voxel generation and everything was fine till a dreaded UE4 crash

!AssertLog="Assertion failed: (Index >= 0) & (Index < ArrayNum) [File:D:\UE_4.8\Engine\Source\Runtime\Core\Public\Containers\Array.h] [Line: 678]

this line pumps this

checkf((Index >= 0) & (Index < ArrayNum),TEXT("Array index out of bounds: %i from an array of size %i"),Index,ArrayNum);

Which makes sense

Code in question

Video Link - from where i was watching it

The problem isn’t your UE version, it’s that you are accessing an array out of bounds.

Somewhere you are calculating an index and accessing into “chunkFields” but that index is larger than the array size (or you’re trying to pass an index < 0).

You need to add a breakpoint or some code to try and catch that bad index value and see how you are calculating it.