I crash randomly when playing Agrarian Skies 2 on my server.

Forge: forge-10.13.3.1387
AS2: 1.0.39
ModTweaker: ModTweaker 2-0.8.0
MineTweaker: MineTweaker3-1.7.10-3.0.9C

Log: http://pastebin.com/3p8cTy2B
*I am using Fastcraft and Optifine, but I can reproduce without.