[2021] Path of Champions bugged?

Hi! Welcome to LoR.

Gangplank summons a card called The Dreadway when he has less than 20 health (and he can also just summon it normally). While that is on the board, all of his Spells, Skills, and Allies deal 2x damage. This might be where that extra damage is coming from. I'd recommend saving spells or units to help remove the Dreadway, or not letting him get below 20 health until you're ready to kill him in one strike.

There's a little eye on the left side of the board (Oracle's Eye) that you can use to preview what will happen from attacks, spells, or skill resolutions, which will be helpful in understanding what's going to happen once combat or spells resolve.