I have seen similar issues with PDFs exported from Pro and the World Hillshade layer set to transparent (about 80%). I actually use it in combination with the Multidirection Hillshade (also set to transparent).
To be honest, I am not sure if this is actually an issue with the way ESRI writes these PDFs with the raster basemaps and transparency from Pro, or a bug in Adobe Reader that Adobe should fix... The issue seems to "shift" when I scroll and pan through the map in Adobe Reader. An area that does not look good at one point, may look good later on when I pan back.
The quadcore Core i7 laptop I am viewing them on has the latest NVidia drivers and a dedicated graphics card with 4GB DDR5 RAM, so I don't think it is an issue with an under resourced laptop.