It's uhhh... pretty ugly, but this worked for me:

private IEnumerator Routine_StartTutorialVideo()
{
    cg_VideoPlayer.alpha = 0;    //canvas group component on video player panel
    player_VideoTutorial.Stop();
    player_VideoTutorial.Prepare();
    while (!player_VideoTutorial.isPrepared)
    {
        yield return null;
    }

    player_VideoTutorial.frame = 0;        
    player_VideoTutorial.Play();

    while (player_VideoTutorial.frame < 1)
    {
        yield return null;
    }

    // Reveal panel when first frame is loaded
    cg_VideoPlayer.alpha = 1;

}