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Troubleshooting 404 and Performance Errors with webpc-passthru.php

24 threads Sep 10, 2025 Plugin → Converter for media – optimize images | convert webp & avif

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Many users of the 'Converter for Media – Optimize images | Convert WebP & AVIF' plugin encounter a common and frustrating issue: their site is flooded with 404 errors for URLs containing webpc-passthru.php, often leading to severe performance lag. This article explains why this happens and provides the most effective solutions to resolve it.

Why Am I Getting webpc-passthru.php 404 Errors?

The webpc-passthru.php file is a core component of the plugin's "Pass Thru" image loading mode. These errors typically occur in a few specific scenarios:

  • The plugin is disabled or removed: When the plugin is deactivated or deleted, the webpc-passthru.php file is no longer available on the server. However, if your site's cache (browser, plugin, or server) still contains HTML pages with the old webpc-passthru.php image URLs, every request for an image will result in a 404 error.
  • Switching from Pass Thru mode: If you change the plugin's "Image loading mode" setting away from "Pass Thru," the file is no longer used, but cached pages may still reference it.
  • Server Configuration Issues: On some servers, particularly those with Nginx or specific security rules, execution of the webpc-passthru.php file may be blocked, resulting in 403 Forbidden or 404 errors.

How to Fix webpc-passthru.php 404 Errors

Based on community reports and solutions, follow these steps to resolve the issue.

1. Clear All Caches (The First and Most Important Step)

This is the most common solution. You must clear every layer of caching on your site to purge the old webpc-passthru.php URLs and allow new, correct image URLs to be generated.

  • WordPress Caching Plugins: Clear the cache in any installed caching plugins (e.g., WP Rocket, W3 Total Cache, LiteSpeed Cache).
  • Server-Level Cache: Clear any cache provided by your hosting provider (e.g., Varnish, Nginx FastCGI Cache). You may need to contact your host for this.
  • CDN Cache: If you use a Content Delivery Network like Cloudflare, clear its cache entirely.
  • Browser Cache: Instruct users to do a hard refresh (Ctrl+F5 on Windows, Cmd+Shift+R on Mac) or clear your own browser cache while testing.

2. Switch to the "via .htaccess" Loading Mode

The "Pass Thru" mode is an alternative delivery method that can be more prone to conflicts. The plugin's default and often more reliable mode is "via .htaccess."

  1. Ensure the plugin is active.
  2. Navigate to Settings > Converter for Media.
  3. Find the "Image loading mode" setting.
  4. Select the option labeled via .htaccess.
  5. Save your changes.
  6. Remember to clear all your caches again after making this change.

3. For Nginx Users: Manual Configuration

If your server runs on Nginx, the "via .htaccess" mode requires manual configuration since Nginx does not process .htaccess files. You must add the provided Nginx server configuration rules to your server's main configuration file. The exact code can be found in the plugin's FAQ. After adding the rules, reload your Nginx configuration and clear all caches.

4. Check for Plugin Conflicts

Some optimization or security plugins can interfere with the webpc-passthru.php file. Try temporarily disabling other plugins to see if the 404 errors resolve. If they do, reactivate them one by one to identify the culprit. Pay special attention to image optimization, security, and caching plugins.

5. If The Plugin Is Deactivated: Regenerate HTML

If you have decided to remove the plugin entirely but are still seeing 404 errors, it confirms that your site's pages are served from a cache. After ensuring all caches are completely cleared, the old webpc-passthru.php URLs should disappear. If you use a page builder or have a static site, you may need to regenerate your pages or posts to update the image URLs within them.

When to Seek Further Help

If you have tried all the steps above and the errors persist, the issue might be related to a specific server security configuration blocking the PHP file. In this case, you may need to consult your hosting provider's support to check the server's error logs and ensure that execution of .php files in the wp-content directory is permitted.

By systematically working through these solutions—primarily focusing on clearing all cache and using the recommended "via .htaccess" mode—most users can successfully eliminate these pesky 404 errors and restore their site's performance.

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