I’ve gotten this Boss Fractal at least 5 times, and never have I received a +1 infusion, I am getting one from Mai Trin (Aetherblade) and Maw still, but not the Molten boss fight. Considering it’s the hardest boss fight (only one you can get 2x agony stacks and insta-downed) it should be awarding 1 or more +1 infusions.