As this needs further detailed investigation and focuses on the case, kindly open up a separate thread only for the preview problem. Give us detailed information about the case and if this is happening on all pages or only a specific page. If a specific one, then gives us the page name.
Also, give us detailed information on results of these tests:
In the secure note give us the URL/User/Pass of your WordPress dashboard and we will follow up the case to the best of our abilities.
Thank you for your understanding.