UNREAL UE4 - Post Processing makes white blur, around moving characters in dark backgrounds, why?

Hi, when post processing is turned on “medium” in “engine scalability settings” , i get White artifacts aroung my character when camera moves fast around it, this problem is only happening when using post processing and i just created a first person scene, everything is at default, i only removed the clouds dome at background, so now its black and it looks like this problem is more obvious now with my dark background, I added an image of my character while moving camera real fast around it so you can see the artifact noise or white blur.

Why this happens? My scene is completly at default do, i´m new to Unreal, please share some steps for fixing this issue. Please help & Thanks