What is happening is the Admin panel, which consists of three sub menu pages disappears when WordFence is active. So he can't go into the Testimonial Basics admin features when your plugin is active,
It's like katb_testimonial_basics_admin.php is not loading. Below is the script to load the admin php file.
if( is_admin() ) {
//load admin functions
require_once( dirname(__FILE__).'/includes/katb_testimonial_basics_admin.php' );
}