I'm running iOS 9.0.2 and recently had to delete the beta because it always instantly crashed-on-open, so I'm running the latest version from the App Store.
I wasn't sure if it was seeing if I wasn't double-tapping before scrolling, so I set all double-tap behaviors to "Do Nothing," but the issue persists.
So, it may have been behaving like a memory leak. It seemed to be getting worse, like unbearably bad, a full second or more from swipe to motion. I force quit the app, restarted it, and the scrolling seems fine now.
I don't know what you can fix at this time; I seem to recall even a reinstall didn't fix it before, but now I'm not sure (I think I would have said as much in my original post)?
If it comes back, I'll update again.