The one-at-a-time interactions, both desktop and mobile, will auto-advance single-select questions as you see below. We've set the one-at-a-time interaction as the default for mobile to decrease the need for scrolling on smaller screens.
You can switch to the standard interaction wish. To do so go to Style > Layout > Desktop Interaction/Mobile Interaction and select the Standard interaction in both places. Or, if you wish to keep the one-at-a-time interaction but disable the fly-in animation aspect we have a workaround documented in our Disable Fly-In Animations for One-at-a-Time Interaction Tutorial.