Skill Attack co-op question

My friend and I are playing co-op campaign with skill attack on as well as iron, mythic, and birthday grunt skulls on. When one of us dies and we go back to the last checkpoint, he, and only he, loses a number of points. I stay the same. It causes him to eventually be overcame by my points just by dying enough. Is this a bug? Is this how it’s supposed to be? Can I fix it?