I am actually not 100% sure if this mod is what scausing it, but i think there's a high chance.
When upgrading from lower quality assemblers, i.e. building rare ones on top of common ones, the rare assemblers are NOT removed from your inventory. In fact it creates an extra rare assembly machine every time you do it.
Should be easy to try and reproduce
Also, in the description of the Assembly machine (if you alt-click on it) it still says that every quality of assembler only has 4 module slots, when they should increment by one per quality.
