doesn’t save taxonomy value

Default code from online generator:

function your_prefix_get_meta_box( $meta_boxes ) {
	$prefix = 'prefix-';

	$meta_boxes[] = array(
		'id' => 'untitled',
		'title' => esc_html__( 'Untitled Metabox', 'metabox-online-generator' ),
		'post_types' => array('post', 'page' ),
		'context' => 'advanced',
		'priority' => 'default',
		'autosave' => 'false',
		'fields' => array(
			array(
				'id' => $prefix . 'taxonomy_1',
				'type' => 'taxonomy',
				'name' => esc_html__( 'Taxonomy', 'metabox-online-generator' ),
				'taxonomy' => 'category',
				'field_type' => 'select',
			),
		),
	);

	return $meta_boxes;
}
add_filter( 'rwmb_meta_boxes', 'your_prefix_get_meta_box' );

When I select term in Untitled Metabox (look at the screenshot https://image.ibb.co/gz3Q6V/bug.png) and push Update there are no term checked in Untitled Metabox, but in Categories (side) is OK.

What is the problem?