Hi @lwskcmi,
Please be aware that when you create a page or post using Cornerstone, a cornerstone data which contains all the element settings are saved as a post meta of the page/post. As soon as you edit the page/post outside of Cornerstone, the changes will not be saved into this cornerstone data and it may even corrupt or remove the post meta indicating that Cornerstone is no longer the primary editor of the page/post. This is one of the reasons that as soon as you get back to edit the page/post in Cornerstone, the content is already empty and looks like you need to start from scratch again.
Be advised that Cornerstone is a page builder. You can also use it to create your posts. once you created the page or post in Cornerstone, it is only editable in Cornerstone. You cannot use the default WP editor or any other page builder. If you do so, then it is best that you create the content from scratch.
Thanks for understanding.