Effects become pixelated within my exported video.

Hello, so I'm having a very frustrating issues where any effects I apply to my video become a pixelated mess after export. I've tried so many export setting and I just cant get it to look at clean as it does in my preview before exporting. My video generally looks really good until some video affects is applied and then the effects looks horrible and leaves a pixelated effect on my video for about 1 second after the effect ends.  Anyone have any idea what's going on? And yes, my source footage format is the same as my export format.