I was experiencing the white line to the right on my iPad as well in horizontal position only. I was using a fixed-position div with a background set to 960px wide and z-index of -999. This particular div only shows up on an iPad due to a media query. Content was then placed into a 960px wide div wrapper.
The answers provided on this page were not helping in my case.
To fix the white stripe issue I changed the width of the content wrapper to 958px. Voilá. No more white right white stripe on the iPad in horizontal position.
