Clean Fotografie pro parallax header issue

Hi - I just purchased the theme mentioned above. I like it so far, but have an issue on mobile with the parallax header image. It looks like the resolution or zoom of the image changes when I start scrolling. I noticed the demo does the same thing, but pc version of the site and mobile emulator in edit mode are smooth. www.dsophotos.com Any way I can adjust something to have the smooth scrolling on mobile? Thank you, John