I ran into this problem on a client’s site and was able to fix it by making sure that the slider and slides within it stretched the full width of the screen. Instead of having margin outside of my slides, I made them full width and added padding on the inside. I think most of the unintended vertical scrolling comes from sliding your thumb across the edge of the screen that isn’t contained by the slider element. This solution may not be possible with all designs, but hopefully can help out in a lot of cases!