[Bug] 9 Lives/Greed mode bug?

Here's a screenshot of my items: https://i.imgur.com/grxr3hO.png

I'm playing Isaac with Greedy mode. Leviathan & Guppy transformation, no mods, 9 lives, chaos item. I picked up 9 lives on the second last floor, then spent my last red heart on a devil deal and stocked up to full HP with spirit hearts on the last floor. I entered the greed fight with curse of the unknown, but I knew I had 12 spirit hearts. Got hit once, and died immediately. Does anyone know what could have caused this, or was it a bug?