I agree with @Malachiman. It not really a Blocs Issue, its a mobile device issue - more specifically, a touch screen issue. In an attempt to limit script execution on scroll events, mobile browsers deliberately don’t support this function. Of course, there are ways to circumvent the limitation. However, you do risk your site visitors suffering performance issues. Here is a recent blog post on the subject:
One of the largest criticisms of the parallax scrolling effect is its poor performance on mobile devices. Parallax effects appear broken or choppy on mobile devices because mobile web browsers are designed to limit script execution upon scroll events.
A good web designer will understand this in advance and plan for a static or mobile-optimized version of the website that essentially “turns off” the parallax effect when the mobile environment is detected. The website will look exactly the same in its static state, we just remove the movement of design elements and the requirement of the mobile browser to call external scripts to perform the calculations their desktop cousins can do more easily.