There is a stupid glitch... while in the soul cairn after completeing the dawnguard main line quests. Went back in to the soul cairn to get the jiub's side quest done and acquire the sumon books. When I acquired the third Reaper Gem Fragment, after leaving the area of the purple floating gem that's above that chest, the blue mist stuff coming off the body and absorbing health into the purple floating gem the damage stopped but the graphics stayed. After killing the reaper, returning to the real world (Valerica's study) that graphics glitch was still there... and makes it extremely difficult to see or attack, etc. Had to revert to a previous cloud save game to get rid of the glitch!!!!!!
This glitch makes the game unplayable and causes seizures in people with epilepsy!!! Be Aware!