Hi there,
Would you please kindly give us an access to your WordPress Dashboard at least so that we can check the case and report you back with the suggestions? Currently, we do not have a way to test the case to know why this is happening in your environment.
I checked the server info which you have posted and the memory limit seems to be ok.
The Visual Composer warning can be ignored as you are using the bundled version. For more information:
Please consider that you can not edit a page both with Visual Composer and Cornerstone. If you create a page with Cornerstone you need to keep using it and vice versa.
I also suggest that you enable the WordPress debugging mode so you may get a better information regarding the error:
https://codex.wordpress.org/Debugging_in_WordPress
And also, I suggest that you check for possible 3rd party plugin conflict, by deactivating all 3rd party plugins except Cornerstone and check the case.
If you still have problems kindly get back to us with the information below using the Secure Note functionality of the post:
- WordPress Dashboard URL
- WordPress Dashboard Username
- WordPress Dashboard Password
- The name of the page to test Cornerstone in.
Thank you