comment-reply.js is not loading

Maybe this helps you out?
Please make a backup from functions.php and add following function.

/**
 * Add .js script if "Enable threaded comments" is activated in Admin
 * Codex: {@link https://developer.wordpress.org/reference/functions/wp_enqueue_script/}
 */
function wpse218049_enqueue_comments_reply() {

    if( is_singular() && comments_open() && ( get_option( 'thread_comments' ) == 1) ) {
        // Load comment-reply.js (into footer)
        wp_enqueue_script( 'comment-reply', '/wp-includes/js/comment-reply.min.js', array(), false, true );
    }
}
add_action(  'wp_enqueue_scripts', 'wpse218049_enqueue_comments_reply' );

Note: see codex on how to enqueue