There is some sort of issue with bigfoot targetting. He will not take damage (from my crusader) approximately 2/3 of the time when a hit definitely should hit him. It did not affect my shadower's boomerang step too bad, most likely because of how big boomerang step's hit range is, but a paladin that I was fighting with apparently had the same issue hitting bigfoot. It seems as if the exact same attack at the same spot would only hit sometimes. It was not "missing" per se as you would see in text if you have bad accuracy, but rather the game failing to register that he was hit at all.
This is intentionally left in the game. It was briefly mentioned in one of the status updates. https://royals.ms/forum/threads/new-source-status-update-2.26660/
turning off ur booster helps, when his back is facing u against the wall, you'll hit him all the time one way to avoid his annoying invi frames
