When attempting to brew a potion of weakness in the latest snapshot you cannot do so. Attempting to brew this potion will yield no results. Both methods of brewing weakness potions do not work, as shown in the screenshots seen below. This is the only potion I have found unable to brew at the moment.
MC-92679
Potion of Weakness Unable to Brew
Resolved
Duplicate
0
Did you try an ordinary Water Bottle with Fermented Spider Eye?