Before starting a new topic with this issue, I decided to read through the forum. I am having the same issues since I updated the theme and cornerstone. I try every possible test in your recommendations and still having the issues with the preview "The preview was unresponsive after loading". The content will disappear if I click "Try Again" so I reload the page instead to not lose the content. Also I noticed the following error when I click X - Edit Page
The error comes from /wp-content/plugins/cornerstone/assets/dist/js/site/cs-body.js.
Also having the same error with WARNING: Binding style attributes may introduce cross-site scripting vulnerabilities; please ensure that values being bound are properly escaped. For more information, including how to disable this warning and I increased the php limit and checked the server with the plugin version, also followed the guidelines for updates.
I don't know if the issue has to do with the fact that the content was build in the old cornerstone and this creates some kind of conflict when is being edited with the new one. If there is any extra info I can provide, please let me know because I want to resolve this issue as well before upgrading the production environment to the latest versions of the theme and cornerstone. I am testing this locally and in a nginx/1.10.3 and v7.0.28-0ubuntu0.16.04.1 environment.