Since automation tracks change various states of the song (like the scroll position or recording playback), you need to reload the song to reset everything so the automation track can start again.
If you need to restart auto-scrolling without resending your MIDI or resetting other things, you can click the document button, manually scroll the lyrics to the top and then click the document button again. Alternatively, you can just manually scroll the lyrics to the top, in which case they will begin scrolling immediately, without the pre-roll.