Minecraft 1.12.2
Mod Version r140

https://paste.dimdev.org/evekuteqav.mccrash

Crashes internal server when finishing smelting an item.

Well this is unusual. I'll look into it soon.

Can't reproduce this whatsoever, the field is no longer named slots, so the crash makes sense. Somehow you've gotten a jar that's half r140 and half... something else.

happening on r151 too... wth is it making it mess up like this?! anyone found a fix?

i doubt this has anything to do with it but i found several mentions for "slot" in the containerFurnaceDouble.class (apparently 7zip can open the jar and notapad++ can sorta read the class files). perhaps thats the class that is somehow merging with an older version? then again, idk much about programming so thats just a guess based off the mention of "slot"

also encountering this issue.
on newest version of additions and forge

https://paste.dimdev.org/parihuhizu.mccrash

The world will not start up now. It will load and then immediately crash.