elementor-missing-term-404-fix.php

<?php
/**
 * Plugin Name:  Elementor Pro – Restore 404s on Non-Existent Term Archives
 * Description:  Fixes a fatal error ("Object of class WP_Error could not be converted to string") and incorrect 200 responses on non-existent tag/category/taxonomy URLs when an Elementor Pro Archive template with a paginated posts widget is active.
 * Version:      1.0.0
 * Author:       https://robertwent.com
 * License:      GPL-2.0-or-later
 *
 * ---------------------------------------------------------------------------
 * THE PROBLEM
 * ---------------------------------------------------------------------------
 * On a site using an Elementor Pro Theme Builder "Archive" template that
 * contains a Posts / Loop Grid / Archive Posts widget with pagination enabled
 * (especially "Load More" / infinite scroll, or with no page limit), visiting a
 * term archive URL whose term does NOT exist — e.g. /tag/does-not-exist/ —
 * produces one of two broken results:
 *
 *   1. A fatal error:
 *        PHP Fatal error: Uncaught Error: Object of class WP_Error could not be
 *        converted to string in .../elementor/core/dynamic-tags/manager.php
 *      ...if the template uses the "Archive URL" dynamic tag anywhere. Elementor
 *      Pro's Utils::get_the_archive_url() calls get_term_link( get_queried_object() )
 *      without an is_wp_error() guard; for a missing term that returns a WP_Error,
 *      which Elementor then tries to cast to a string while generating CSS.
 *
 *   2. Failing that, an HTTP 200 response for a page that should be a 404.
 *
 * THE CAUSE
 * ---------------------------------------------------------------------------
 * Elementor Pro adds a `pre_handle_404` filter
 * (Locations_Manager::should_allow_pagination_on_archive_templates) so that
 * paginated archive templates don't get 404'd on page 2+. With Load More /
 * infinite-scroll pagination (or no page limit) it returns "handled" even on
 * page 1 — for ANY archive matching the template, including URLs whose term
 * doesn't exist. That short-circuits WordPress's own handle_404(), so set_404()
 * never runs: the status stays 200 and is_tag()/is_tax() stay true, which is
 * what exposes the WP_Error in the Archive URL dynamic tag.
 *
 * THE FIX
 * ---------------------------------------------------------------------------
 * Hook `pre_handle_404` at a later priority than Elementor (which uses 10/11).
 * When the request is a term archive (tag/category/custom taxonomy) whose
 * queried object is NOT a real WP_Term, force a genuine 404 right there — at
 * the canonical 404 decision point, before template selection and wp_head, so
 * is_tag() is already false when Elementor renders. Real terms (even empty
 * ones) and legitimate paginated archives are left completely untouched.
 *
 * Drop this file into wp-content/mu-plugins/ (it loads automatically). It is
 * harmless if Elementor Pro is not installed.
 * ---------------------------------------------------------------------------
 *
 * @package ElementorMissingTerm404Fix
 */

if ( ! defined( 'ABSPATH' ) ) {
	exit;
}

add_filter( 'pre_handle_404', 'em404_force_404_on_missing_term', 99, 2 );

/**
 * Force a proper 404 when a term archive's queried object can't be resolved.
 *
 * @param bool      $handled  Whether a plugin has already declared the request handled.
 * @param \WP_Query $wp_query The query that triggered handle_404().
 * @return bool True if we've handled it (as a genuine 404), otherwise the value unchanged.
 */
function em404_force_404_on_missing_term( $handled, $wp_query ) {
	// Only term archives: tag, category, or any custom taxonomy.
	if ( ! ( $wp_query->is_tag || $wp_query->is_category || $wp_query->is_tax ) ) {
		return $handled;
	}

	// A valid term archive resolves to a WP_Term. Anything else (null / WP_Error)
	// means the term doesn't exist, so this should be a 404.
	if ( $wp_query->get_queried_object() instanceof WP_Term ) {
		return $handled;
	}

	$wp_query->set_404();
	status_header( 404 );
	nocache_headers();

	return true; // We've handled it — as a real 404.
}

Blog post: Fixing Elementor Pro Soft 404s (and a Fatal) on Non-Existent Tag and Category URLs