Hello Dear,
I found this problem when I attention to quality of images after enlarge them in single product page!
The image becomes a bit blurry after enlarging In a fraction of a second!
I have visited the URL you provided. Please use the product images of higher resolution to make the zoom option to work absolutely fine. Then Go to Appearance >> Customize >> Product images >> Images Crop >> the value of the crop should be Smaller than the actual
images for it to work absolutely fine.