Cornelis Scheltinga

I agree with daniel27lt!

Fixed it:

$bar_key = null;
	$page_id = 'none';

if ( is_page() && !is_front_page() ){
		$bar_key = 'cs_bar_pages';
		$page_object = get_queried_object();
		$page_id = get_queried_object_id();
	}
	else if ( is_front_page() ) {
		$bar_key = 'cs_bar_homepage';
		$page_object = get_queried_object();
		$page_id = get_queried_object_id();
	}

$args = array(
		'post_type' => 'notifications',
		'posts_per_page' => 1,
		'orderby' => 'menu_order',
		'order' => 'ASC',
		'meta_query' => array(
			'relation' => 'OR',
			array(
			'key' => $bar_key,
			'value' => 'yes',
			),
			array(
			'key' => 'cs_bar_specific_pages',
			'value' => $page_id,
			'compare' => 'LIKE',
			),
			array(
			'key' => 'cs_bar_specific_posts',
			'value' => $post_id,
			'compare' => 'LIKE',
			),
		)
	);

Already got it. It was the second array which causes the trouble.
It should have ‘value’ => ‘0’, instead of ”. Strange why it worked on my localhost anyway.