When you are autoscrolling through a song, the live bar button appears as a play/pause function. This allows you to stop autoscrolling halfway through a song and restart it later.
If you'd like to reset autoscroll, just double tap on the autoscroll live bar button. This will return autoscroll to the top of the song and continue autoscrolling.
This same logic also works for audio playback using the live bar button!