html/php content not rendering on view source until page refresh

I’m integrating an iframe with dynamic php content in its src on a checkout congratulations page. When the process is complete the iframe with code shows in Firebug, but not on view source in the browser. If I refresh the page the content shows in the browser view source. This, is what I believe, is causing the integration to fail because the iframe is not being picked up by the online service we are using.

Its a WordPress so the final page calls get_header(); then html/php then get_footer();. Everything in between the header and footer does not show on the view source until I refresh the page, very odd. I tried googling but I found nothing and I’m not sure what even may cause it or where to begin.
Any experience with this?

Edit.
below is the code, everything inside of and including section1 div does not show in view source.

<?php get_header(); ?>


<div class="section1">
  <div class="container">
    <div class="row">
      <div class="col-lg-12 col-md-12 col-sm-12">

        <iframe here>

      </div>
    </div>
  </div>
</div>




<?php get_footer(); ?>

Edit:
I still don’t know why, but it had to do with destroying all PHP session and browser cookies. Time to mark this one closed. If I ever figure out why,
I’ll edit this question.