(Author here) To clarify, we don't actually replace it automatically - we show a pill notification that new stories are available. You can either choose to tap it and see the new feed, or ignore it and continue with what you were doing
Great for the web team if they are doing a better job than the mobile team I guess.
I also see if it the app is running in the background and I switch back over to IG. I can be in the middle of my feed and scrolling and after a few seconds it refreshes and I lose my spot.