Error: The aria-labelledby attribute must point to an element in the same document.

I commented out the aria code to get a site to validate until I can run this one down. It was lines 142, 145, and 161 in views_slideshow/contrib/views_slideshow_cycle/theme/views_slideshow_cycle.theme.inc.

  $widgets = $vars['options']['widgets'];
  if (isset($options['top']['views_slideshow_pager']['enabled']) && $options['top']['views_slideshow_pager']['enabled']) {
 //   $aria = "aria-labelledby='views_slideshow_pager_field_item_top_${vss_id}_";
  }
  else {
 //   $aria = "aria-labelledby='views_slideshow_pager_field_item_bottom_${vss_id}_";
  }


  $items = array();
  $slideshow_count = 0;
  $rendered_rows = '';
  $last_slide = ceil(count($rows) / $items_per_slide);
  foreach ($rows as $count => $item) {
    $items[] = $item;
    if (count($items) == $items_per_slide || $count == (count($rows) - 1)) {
      $rendered_rows .= theme(views_theme_functions('views_slideshow_cycle_main_frame_row', $vars['view'], $vars['view']->display[$vars['view']->current_display]), array(
        'vss_id' => $vss_id,
        'items' => $items,
        'count' => $slideshow_count,
        'view' => $vars['view'],
 //       'aria' => $aria . $slideshow_count . "'",
        'last_slide' => $last_slide,
      ));
      $items = array();
      $slideshow_count++;
    }
  }

  $vars['rendered_rows'] = $rendered_rows;

Investigated and super easy proper fix - though obviously your fix prevents that error as well.
So the problem is that the aria value is added even if there isn't a pager when it should only be added when there is a pager.

Thanks for the report and details! Fixed in dev, will be in 7.x-3.9