Posts with the same page URL

You can force URL Manager to prioritize one specific post type above others (assuming the same URL is used by both “post” and “page”).

function pm_control_duplicates( $excluded, $element_object, $old_query, $pm_query ) {
	global $permalink_manager_uris;

	// Which post type should be prioritized above others?
	$priority_post_type = 'page';

	// Check if there are any other items with the same custom permalink
	if ( ! empty( $pm_query['uri'] ) && ! empty( $element_object->ID ) ) {
		$uri = $pm_query['uri'];

		// Get IDs of other content items
		$ids = array_keys( $permalink_manager_uris, $uri );

		$duplicate_has_priority_post_type = false;

		// Check if any of duplicated posts belongs to priority "post_type"
		foreach ( $ids as $id ) {
			if ( ! is_numeric( $id ) ) {
				continue;
			}

			$post_type = get_post_type( $id );

			if ( $post_type == $priority_post_type ) {
				$duplicate_has_priority_post_type = true;
				break;
			}
		}

		// If the detected custom permalink is used by both priority "post_type" and another content_type exclude it from the detect function
		if ( $element_object->post_type !== $priority_post_type && $duplicate_has_priority_post_type ) {
			$excluded = $element_object->ID;
		}
	}

	return $excluded;
}
add_filter( 'permalink_manager_excluded_element_id', 'pm_control_duplicates', 10, 4 );