Only First Group Field Appears

This is the code I'm using:

    $meta_boxes[] = array(
        'title'  => 'Album Tracks',
        'pages'   => array( 'post','page' ),
        'fields' => array(
            array(
                'id'     => 'standard',
                // Group field
                'type'   => 'group',
                // Clone whole group?
                'clone'  => true,
                // Drag and drop clones to reorder them?
                'sort_clone' => true,
                // Sub-fields
                'fields' => array(
                    array(
                        'name' => 'Track name',
                        'id'   => 'text',
                        'type' => 'text',
                    ),
                    array(
                        'name' => 'Release Date',
                        'id'   => 'date',
                        'type' => 'date',
                    ),
                    array(
                        'name'    => 'Genre',
                        'id'      => 'genre',
                        'type'    => 'select_advanced',
                        'options' => array(
                            'pop'  => 'Pop',
                            'rock' => 'Rock',
                        ),
                    ),
                ),
            ),
        ),
    );

I have now tried installing the plugin normally via the WP Plugins page, but the result is still the same. It doesn't work at all. Please get back to me asap. I'm on a tight deadline and could have just done this using CMB2 for free. I invested $50 in this extension to save time. It has to work.