I had the cupcake item which provides 1 energy, but permanently removes any card played after the 3rd each turn from your deck. I had an item which transformed cards in combat, and the game crashed every time when I play one of the transformed cards after the 3rd so the cupcake item removes it.

Obvious take would be that the functionality of the cupcake item does not consider that when trying to purge a card. Maybe it is the other items fault (it is modded, Grand Snecko Eye, grants 1 energy but transforms 2 cards each turn).