We use a UIScrollView but manage our own virtualization and when fast scrolling kicks in tvOS adds a secret child to our UIScrollView of type _UIFocusFastScrollingIndexBarView and gives it focus. I don't see shouldUpdateFocus being called for when this happens so I can't stop it. This is wreaking havok with our input and virtualization systems.
We've tried scrollView.indexDisplayMode = .alwaysHidden but that doesn't stop this.
Correction, scrollView.indexDisplayMode = .alwaysHidden appears to stop the swipe on the right edge gesture but it does not stop the multiple-fast-swipes gesture. tvOS will still go into fast scroll mode and give focus to the widget that's hidden. I'll file a Radar.