Seem to be having issues in child theme

Did you ever get DesktopServer working to configure metabox to work with it?
On my Linux system I have switched over to VVV, but still using DS on my office Windows machine

Well, the issue only occurs for themes it seems, because it does not have an issue when I use settings in plugins.

Whilst you are around, is there a way to make the tabs extensible?

I was trying this

$meta_boxes[] = array(
		'id'             => 'options',
		'title'          => __( 'Extensions Options', 'fl-builder' ),
		'settings_pages' => 'builder-extensions',
        'tabs'           => array(
            'general'    => array(
                'label'  => __( 'General', 'fl-builder' ),
                'icon'   => 'dashicons-admin-tools',
            ),
            'popup'    => array(
                'label'  => __( 'OnClick Popup', 'fl-builder' ),
                'icon'   => 'dashicons-admin-plugins',
            ),
            do_action('extensions_tabs'),
        ),