Yes, you can absolutely "lose points" if the average score & high score changes & bumps you into a lower bracket. Your points are based on what bracket you're in... on the flip side, you can also gain points by doing nothing at all. I ran Heliostat solo on a low difficulty, just to check it off the list. I was in the 1st bracket for a few days... but apparently people are doing terribly at the mission & the "average score" when down, thereby putting my score "above average" and bumping me into the 2nd bracket. It was a funny thing to watch. I wonder if ppl will catch on & purposely run poorly several times, just to drag the score down... then have one really good run on the last day, to lock in a good score.