FOR THE LOVE OF GOD. Take those down and compress them! PNG at least.Stumbled on this by a keep, ball of particles glitched, 4.8 FPS, my guess is I got (lucky) and found this. Willing to bet when fps hit the floor one of these is off map somewhere.
There is an area in the Alik'r Desert, Southwest of Sentinel I believe, where the quest is to cleanse the water containers. There are dead assassin beetles there with some kind of smoky, glowing haze around them. When your character looks at them FPS drops dramatically but when you look away the rate comes back up. Not sure if they are related or not but might be worth a look into.