If your site displays content based on a master layout and you try to preview the content, Preview mode does not show the updated content on the PageBuilder layout.
The HTML content is not compatible with the PageBuilder templates.
To check your content type, look at the second column in the content listing section of the Workarea.
To view the HTML content on the page layout, go into the page layout itself, and preview it there. The system pulls in the required variables (such as the page ID and the Content IDs) that you have associated with the template. This lets you successfully preview the content on a PageBuilder page.
<%= heading %>