Thank you for the credentials, but I can not connect with the FTP account, please check.
Let's enable the
WP_DEBUG to try to log the error. Please add this on your
define( 'WP_DEBUG_LOG', true );
define( 'WP_DEBUG_DISPLAY', true);
Add this before the line:
/* That's all, stop editing! Happy blogging. */
I also notice, that your X theme is few updates behind, please update the X to 6.1.6 version. And also your WordPress (4.6.11) that is outdated. Please update that to the Wordpress latest version. This could be indirectly the caused of the issue.
Updating Your Themes and Plugins
I would strongly advise that you do this on a staging server first.
And please confirm that you already did the plugin confict test suggested above, if not please do so.