The submit button is part of the repeat selection, so its name has been changed to be dynamic.
change:
<input class="button" style="font-family:Arial;" type="submit" name="updateshow_<?php echo $RepeatSelectionCounter_1; ?>" id="updateshow_<?php echo $RepeatSelectionCounter_1; ?>" value="Update Slides">
to:
<input class="button" style="font-family:Arial;" type="submit" name="updateshow" id="updateshow" value="Update Slides">