Thanks for sharing the details.
Note: Please never share login details in public. Always use secure note feature to share login/confidential information, so that details are in between you and Themeco staff. I have moved the login details into secure note.
I installed a plugin to check the server configuration. I see that you are using PHP version 5.6. I suggest you to get in touch with the hosting provider and ask them to update PHP to atleast version 7. WordPress recommends you to run PHP version 7.2 or greater. https://wordpress.org/about/requirements/
Although you have shared the login details, I am not allowed to do deep troubleshooting without taking due permission from customer. So I suggest you to please test for plugin conflict from Plugins > Installed Plugins and deactivate all the active plugins other then Cornerstone. After that under Pages > All Pages try and edit page in Cornerstone to see if builder and Content is loading. If it's loading then you need to reactivate one plugin at a time to narrow down which one is causing the issue. To help you do that I have recorded a screencast, please take a look. https://cloudup.com/cdpVPwWEgN4
In case problem is still there, please give us the permission to test the website further. While we are testing, there may be some issues with the layout temporarily.