For a while, I’ve noticed that when I implement scrollable fixed or absolutely positioned elements on top of everything, the feel is just a little “off” on mobile. I’m used to that swipe/wait/scroll, as opposed to swiping … and the scroll immediately stops when I do.
I haven’t a clue why this behavior wouldn’t be the default, but give these two properties a try:
overflow-y: scroll; -webkit-overflow-scrolling: touch;
(And make sure the overflow is scroll and not auto. Just … ’cause … that’s the way it works.)