I was using an enchanted diamond chisel on all the mods 6 (1.16) and right clicked with it in the offhand, when I tried to shift-click a stack of blocks out of the chisel menu I knocked the whole server down
Minecraft crash popup:
The game crashed whilst container click
Error: java.lang.ClassCastException: team.chisel.common.block.ItemChiselBlock cannot be cast to team.chisel.api.IChiselItem
Exit Code: -1

Ye had the same crash happening in enigmatica 6 expert (dev branch). Link to crash report: https://paste.ee/p/6nCYy

Had a time in a bottle in main hand, but had it happen with empty main hand too.

Could you post a crashlog that doesn't expire? I can't see where this would happen.

Could you post a crashlog that doesn't expire? I can't see where this would happen.

While I may not be the one who made this issue, I've had something very similar happen with me holding an iChisel in my offhand and nothing in my main hand. When I attempted to use the chisel my game froze for over 10 minutes before it finally died: https://pastebin.com/R9cGGJbx

This crash only occurs when holding a chisel in your offhand, otherwise it works perfectly fine. This crash also does not appear to happen in the 1.12.2 version of the mod.