Thanks for writing in. The issue here is most probably version incompatibility with the latest version of WordPress and outdated X, Cornerstone and Visual Composer (now known as WPBakery Page Builder).
Themes and plugins need to be updated to be compatible with WordPress amongst other important reasons like security. With that said, please backup your site first and uninstall Cornerstone and Visual Composer.
Next, since you’re using a very old version of X, you need to manually update it first. You can read the Manual Update instruction in our Setup - Updating Your Themes and Plugins at https://theme.co/apex/forum/t/setup-updating-your-themes-and-plugins/62
You might also need to revalidate X as we have changed our validation system a few versions after the version you’re using. You can read Product Validation process at https://theme.co/apex/forum/t/setup-product-validation/55
During the product validation stage, X will automatically reinstall Cornerstone for you.
After that, reinstall Visual Composer in X > Validation.
You can let us know if the issue persists after that.
Hope that helps.