Label Disappears with Custom Meta Query

Hello,

I’m trying to add a custom meta query to my shop. Whenever I do, the Advanced Labels disappear completely. Why does this happens and how could I go about fixing it? Here’s the custom meta query I’m working with:

add_action( 'pre_get_posts', function( $query ) {

	if( is_admin() ) {
		return;
	}

	if( isset( $_GET, $_GET['in_stock'] ) ) {

		$meta_query = (array)$query->get( 'meta_query', array() );
		$meta_query[] = array(
			array(
				'key'		=> '_stock_status',
				'value'		=> 'instock',
			),
		);
		$query->set( 'meta_query', $meta_query );

	}

} );