1. I encountered this issue on PC/Steam
2. I was playing Alone
3. I was playing as Wulfgar
4. No workaround that I know of aside from where death boundaries are.

I was going back through the "Companions of Ice Wind" chapter, Act 1 just for some higher tier loot on difficulty Champion. Made it through as normal until I was fighting the verbeeg at the end of the level, I cleared out the other enemies to have a 1v1 and approached him. He did the animation for pulling out the flagpost and slamming it down, but I was mid-air slam attack (basic heavy combo that causes hammer to glow golden when attacking) he slammed the flagpost as soon as I was on the ground, but instead of me taking damage from being hit, my character glitched/clipped into the verbeegs feet. I wasn't able to move or roll away from it when it happened, but less than a second later it registered that the verbeeg wasn't on solid/stable ground, so it auto/insta-killed the boss even tho it still have more than half its health.
Just figured this could be looked into to make sure other characters aren't clipping into enemies and causing main big bosses to die without a fight. Unfortunately I don't have a clip to attach but I will be attempting to do it again while recording to see if it happens and will attach it later if possible.