function willer_custom_meta_portfolio_standar() {
	global $post;

	if(!empty($post))
	{
		$pageTemplate = get_post_meta($post->ID, '_wp_page_template', true);
		if($pageTemplate == 'template-pages/page-portfolio-standar.php' )
		{
			add_meta_box(
				'page-portfolio-standar-meta-box', // $id
				esc_html__('Customize Portfolio Standar','willer'), // $title
				'willer_portfolio_standar_meta_callback', // $callback
				'page', // $page
				'normal', // $context
				'high'); // $priority
			}
		}

	}
	add_action( 'add_meta_boxes', 'willer_custom_meta_portfolio_standar' );

The problem also occurs with WordPress 4.9.8 using Gutenberg,
using the classic editor the problem is not there.
I think it’s because Gutenberg uses Ajax to save the options.
Do you have any suggestions to solve the problem?
Thank you