PDF scrolling takes long to render new part. They are left blank and then updated.

ZZYSonny  Am actually not too certain that this can be fixed by MS.

It is just the way the browser renders webpages not as a whole bur rather in bits.

EdgeHTML used to render the whole webpage/pdf as a single image. This is a very rudimentary way of explaining it but that was one of the major advantages of the MS approach.