We would first like to know if there are no third party factors that is causing the issue. With that said, please:
1. Update to the latest version of X and Cornerstone. I see X 6.5.3 and Cornerstone 3.5.3 are used in your site. You can see the latest versions in our Changelog. Please also follow the best practices in updating themes and plugins.
2. I see you’re using a child theme, please switch to the parent theme.
3. Deactivate all third party plugins except the one that you mentioned.
4. Give us WordPress Admin and FTP access in a Secure Note
Please also note that we do not have support for third party plugins. What we’ll do is check if our products are causing the issue and gather information for our developers. We might provide some guidance or fix but just note that it’s not a guarantee.