Crash report is here https://pastebin.com/jjiWvjyA

Sorry if this is something to do on Chunky's end but I figured I'd make an issue here first, noticed this happening when trying to pre-gen on a larger pack, isolated the pack down to just Chunky, Coroutil, and Weather and saw the same results. Server stops and hangs at around 3-7% on pre-gen progress for a 2500 block radius.

Interestingly enough, while writing this issue I tried Chunk-Pregenerator by Speiger, and it seemed to complete a similar pregen load no problem, so this specifically might be an issue with Chunky.