Hello,
Thank you so much purchasing our theme and contacting our support center.
Do you have any additional plugin installed except ones that come with our theme? Did you make any changes or customization in our theme?
Please, turn on debug mode by changing define('WP_DEBUG', false);
to define('WP_DEBUG', true);
in the wp-config.php file to see all PHP errors. If after enabling this mode you still don’t see any errors on your category page contact your server providers and ask them to provide you with all server error logs.
Write us about all these points so we could better understand the problem and try to help you ASAP.
Kind Regards
XTemos Studio