Hi,
Did you ever solve this issue because I am experiencing the same thing. I created a custom post template so I thought I just messed it up, but on a whim I tried creating a test post with the default template and just some text. The content created with Cornerstone is not showing. It shows the structure (header, footer, comment section, etc), but no content.
I tried making a page and the same thing happened. However, you can see content created with Wordpress editor. Previous pages made with Cornerstone still show fine as long as I don’t edit them.