Check your IA markup, I noticed that an inserted gallery had an extra figure tag, within the parent figure tag, it was like:

<figure class="op-slideshow">
    <figure class="op-slideshow"></figure>  <!-- THIS WAS THE ERROR -->
       <figure>
          <img src="1.jpg">
       </figure>
       <figure>
          <img src="2.jpg">
       </figure>
</figure>