Salient 8.5.4 is Now Compatible with Woocommerce 3.3.1 . Kindly update the Theme if you have updated Woocommerce . 

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“Lightbox to open an embed file”

You'd need to do an inline content lightbox by adding an id onto your div like this (just add this on the same page as your link in the text editor)

<script type="text/javascript" src="http://Myserver.com/blah.js"></script>
<div id="lightbox-content" style="width:600px; height:500px;">
  <object width="600" height="500" style="display:none;">
     <param name="host_url" value="http://Myserver.com" />
     <param name="name" value="ABC/XYZ"/>
   </object>
</div>

And then using a link like this:

<a href="#lightbox-content"> link </a>

Your could also hide the initial div from displaying outside of the lightbox with css

#lightbox-content {
  display: none;
}

Cheers