Hello There,
Thanks for providing the information. Can you confirm that you are fully updated? (Theme and Plugins)
Most of the time, out dated theme and plugins will create issues in your site.
Our latest versions are:
X Theme: 4.6.1
Cornerstone: 1.3.1
You can find the latest version numbers here: (http://theme.co/changelog/) Then you can compare them to what’s installed on your site. If you find anything to be out of date, you can review our update guide.
And since you have installed a caching plugin W3 Total Cache, please keep in mind that after doing every updates, always remember to clear all caches when updating so that the code from the latest release is always in use. This will help you to avoid any potential errors.
Hope this helps.