When Heartfire Hero died with power 3, opponent's (egnaroja) life total was at 4, and remained at 4. I saw no in-game reason for the opponent not to take the damage. Then opponent cast Vraska, Betrayal's Sting and use it to draw a card to proliferate and lose 1 life, their life total went from 4 to 0 and they lost.
They would never have taken that action to kill themselves if the life total had been displaying correctly.