Fix WordPress current_page_parent for Blog and Custom Post Type Archive Menu Links

functions.php

/**
 * Checks the current page to see if current_page_parent should be removed from the blog link or added to a cpt archive pagelink
 */
function cr0ybot_cpt_menu_highlight( $classes, $item, $args ) {
	// Remove current_page_parent from Blog if not on a post
	$cpp = array_search( 'current_page_parent', $classes );
	if ( $cpp !== false && $item->type === 'post_type' ) {
		$qo = get_queried_object();
		if ( ( $qo instanceof WP_Post && $qo->post_type !== 'post' ) ||
	 		$qo instanceof WP_Post_Type && $qo->name !== 'post' ) {
			array_splice($classes, $cpp - 1, 1);
		}
	}

	// Add current_page_parent for cpts
	else {
		$pt = get_post_type();
		if ( $pt !== 'page' && $item->object === $pt ) {
			$classes[] = 'current_page_parent';
		}
	}

	return $classes;
}
add_filter( 'nav_menu_css_class', 'cr0ybot_cpt_menu_highlight', 10, 3 );