You'll have to ask the Facebook app developers about that. It's never been all that great. I'm usually just happy if a particular version of the app doesn't crash randomly, my expectations have become that low for it.
With the latest release when I'm scrolling down and I pause for a second, sometimes it scrolls up a post or two on its own. So weird. It's also not consistently smooth.
The app has never really been polished and flawless.
The Facebook app is a whole lot faster than it was a year or so ago. I wish I could make more edits from within the app. Removing a friend from the newsfeed has to be done on Safari or on a puter.
With the latest release when I'm scrolling down and I pause for a second, sometimes it scrolls up a post or two on its own. So weird. It's also not consistently smooth.
The app has never really been polished and flawless.
I think the scrolling occurs on the Newsfeed (or in groups) when one of your friends posts something new. It seems to be a constant update, so it will appear to scroll up as the Newsfeed gets longer (when another post is made). It annoys me at times too, since we can obviously refresh on our own, but it isn't too bad, and I can usually find the post I was looking at, since it is usually just a post or two higher/lower.
I do think the current Facebook app is much better than prior versions. It seems a little more organized, and I'm glad they finally allow you to edit posts and post photos within comments on the phone now.