So I have a hopper feeding and iron furnace, and a hopper sucking the material out of it.

Somehow it's giving me 4 bars per 1 ore with no upgrades in it.

With some testing it only seems to be duplicating copper

What version of the game and mod? The versions I am constantly updating (1.16.5 and 1.18.1) don't have this bug, because I have already fixed

It is 1.18.1 and I believe it would have been the latest version of your mod about mid to late December when I originally downloaded

I'll grab some screenshots or video once I'm off work

I didn't put that to fix this bug in the changelog, but I believe it was in version 1.18.1-1.2 of the mod that I fixed this bug, which was released on January 4th

No need to show the screenshots, just update the mod to the latest version(1.2.2), which already had it fixed