When having points in the smithy skill, large furnaces and small refinerys process the materials (mostly) one stack at a time.
For example: If i split up my ore in 15 stacks, they process at the same rate as long as i don't have any points in smithy. But as soon as i put points in smithy the ore is processed one tack at a time.
Ver. 1.3.9 & 1.4.0 Smithy-points cause large furnace and refinery to burn materials uneven.Not An Issue
There was a discussion about this in our discord and how the smithy skill works and if other mods are used such as furnace splitter or something like that. There is also a discussion on here about it as well that may explain what's happening in your situation:
https://umod.org/community/xperience/38795-smithy-confusion-and-possible-issues
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