Okay, I know the probabilities, and it's very suspect when someone says the RNG hates them, or whatever. However, I just smelted 3 full loads of chalcopyrite in my 3 smelters. I have deep artifice, so I should have a 12% yield, but that's still an 88% chance of nothing per piece of ore, even if everything is working properly.
But 75 ore all getting nothing comes to a 0.007% chance.
I would be inclined to chalk it up to an extremely rare chance because I'm well aware that those can happen. However, this isn't the first time, and having it happen twice strikes me as very unusual.