Are your devices Apple devices by any chance? We had a similar bug reported at work recently, and it turned out that Windows browsers will always show scrollba

Are your devices Apple devices by any chance? We had a similar bug reported at work recently, and it turned out that Windows browsers will always show scrollbars but the ones running on OS X/iOS will hide them until you start scrolling. To turn them on in OS X, go to System Preferences > General and set Show scroll bars to "Always".