1.16.5
Forge 36.2.39
BetterFurnacesReforged-1.16.5-1.9.7.jar
Ultimate-Furnaces-BFR-1.16.5-1.3.1.jar

How:

1. Load up a world
2. Place an Ultimate Furnace or an Ultimate Forge (both will make it crash)
3. Right Click on the furnace to use it
4. CRASH

CRASHLOG: https://pastebin.com/ZCzsm5E8

The Ultimate Furnaces addon does not yet have total compatibility with versions of Better Furnaces Reforged after the date of its release, it will soon be updated to add this support

For now, don't use this addon, if you're using it in survival mode, avoid it until the update

oof, i was actually pretty far into my survival run the moment I discovered this crash, Thankfully this crash isn't world-breaking.

Fixed in Ultimate Furnaces 1.19.2-1.0, 1.18.2-1.0.2 and 1.16.5-1.3.2