On Neoforge, the Concocter can consume resources but not produce an output. Repro steps:

1. Fill Concocter with ingredients for a Night Vision Tincture (8:00): 1 moon dust, 1 water-filled skyglass flask, 1 redstone dust, 1 nether wart, 1 golden carrot.
2. Concocter immediately begins working, produces the Tincture.
3. Without removing the Tincture from the Concocter, put the same ingredients into the Concocter again.
4. Concocter immediately begins working & produces another Tincture, but the output slot contains only 1 Tincture (they don’t stack, and there’s nowhere else for the new Tincture to go, I guess.)

I am actually not sure if it the new tincture is overwriting the output slot, or if it’s the newly-made Tincture that’s just vanishing from existence, since they were the same type in my example.