I don't see anything wrong on the first image but I could be overlooking? Whereas for the others, it's possible the designs are intended for R6 use, not R15 if the glitch happens to disappear.

 

the knees glitch within itself, and look super pixelated when walking or running. Well, i said above that switching to R6 in the avatar creator removes it, but once i spawn into a game (any game) it comes back.

 

That is something to do with R15 animations. The current animations are not perfect as you can see in the images the legs are clipping together. I think i remember Roblox said that they were working on improving the animations by making the body parts bend instead of having certain body parts separated for animating. It doesn't show up in R6 because that uses a simpler animation that doesn't involve separating the body parts for animating.

 

Ive had this issue quite a lot. I think its from the R15 animation.

 

You have to close the Roblox browser and come back again