Hello There,
If the message when debug is set to false and more message when set to true, could you please provide us your site access and ftp access so that we can investigate this issue? I am guessing that this may have come from a custom code or from the Rev Slider plugin as well.
By the way, are you using the updated versions? Most of the time, out of date theme and plugins can create issues. Our latest versions are:
- X theme 5.2.2
- Cornerstone 2.1.3
- Rev Slider 5.4.6.2
This latest release contains fixes for several issues so be sure to check out the changelog (http://theme.co/changelog/).
After doing the updates, always remember to clear all caches (if you are using WP Rocket, WP SuperCache or W3 Total Cache) when updating so that the code from the latest release is always in use. This will help you to avoid any potential errors.
Please let us know how it goes.