First encountered this yesterday when I smelted ~1020oz of Gold and became a ~27oz ingot back.
I lost 6 hours of progress there since at the very same time, the autosave happened.
I loaded my save from 6 hours ago and tried it again, same result.
The ingot output is not aligning the expected ingot weight output.
The video showcasing it is attached in the Link, as well as the save file from my world.
To explain the video shortly, it shows how I smelt 827.753oz with a loss of 20.694oz, making the expected ingot weight 807,059oz.
However, it returned a 167.0 oz ingot.
I should clarify for the video, that the other ingots came from a time playing where the bug didn't occur and I had the smeltery size on the second largest.
Unlike this time where I unlocked the infinite smelting size.
I've reinstalled the game, I've let steam run over it to find broken files, but both things didn't help.