Thanks for writing in! Before anything else, please update X theme to the latest version first.
X 5.1.1 is now available in automatic updates! This 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.
After updating everything, please clear your phone's mobile browse cache or use private browsing mode and test your site again.
Please let us know how it goes.