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Troubleshooting Common Autoptimize Cache and 404 Errors

27 threads Sep 16, 2025 Plugin → Autoptimize

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Autoptimize is a powerful tool for optimizing your WordPress site's performance. However, users sometimes encounter issues where cached files are not properly cleared, leading to 404 errors or even site breakage. This guide will help you understand why these problems occur and how to resolve them effectively.

Why Do These Cache and 404 Errors Happen?

The most common cause of persistent 404 errors is a conflict with other caching layers. When Autoptimize generates new optimized files, older cached versions might still be served by another page cache (e.g., from your hosting provider, a plugin like WP Super Cache, or a CDN like Cloudflare). This mismatch means browsers try to load files that no longer exist in Autoptimize's cache folder, resulting in 404 errors.

Other potential causes include:

  • The cache directory (wp-content/cache/autoptimize/) having incorrect file permissions.
  • A very large cache that times out when trying to clear it via the admin toolbar.
  • Another plugin or theme interfering with Autoptimize's uninstallation or cache-clearing process.

Step-by-Step Troubleshooting Guide

1. Clear All Caches Thoroughly

This is the most critical step. You must clear every cache that sits between Autoptimize and the user's browser.

  • Autoptimize Cache: Go to Settings → Autoptimize and click "Save Changes and Empty Cache". This method is more reliable than the "Clear CSS/JS Cache" button in the admin toolbar, which can time out on large sites.
  • Other Plugin Caches: Clear the cache in any other caching plugin you use (e.g., W3 Total Cache, WP Rocket).
  • Server/Host Cache: Check your hosting control panel for an option to clear the server-level cache. Contact your host if you are unsure.
  • CDN Cache: If you use Cloudflare or another CDN, purge its cache entirely.
  • Browser Cache: Finally, do a hard refresh (Ctrl+F5 or Cmd+Shift+R) in your browser to ensure you are loading the latest files.

2. Enable 404 Fallbacks

Autoptimize includes a feature to help prevent 404 errors from breaking your site.

  1. Navigate to Settings → Autoptimize.
  2. Click on the "Advanced" tab.
  3. Ensure the checkbox for "Enable 404 fallbacks?" is selected.
  4. Save your changes.

When enabled, this feature attempts to serve a non-optimized version of a file if the optimized one is missing, preventing a complete failure.

3. Check for File Permission Issues

If Autoptimize cannot write to or delete files from its cache directory, errors will occur. The wp-content/cache/autoptimize/ folder should be writable by your web server. Typically, this means setting permissions to 755 for directories and 644 for files. You may need to contact your hosting provider to verify and correct these permissions.

4. Investigate Plugin Conflicts on Uninstall

If you encounter a critical error when trying to delete or deactivate Autoptimize, it is likely due to another plugin or theme hooking into its code.

  • Check your WordPress admin email for an automatic error message from WordPress core, which should contain specific technical details.
  • Ask your hosting provider to check the server's PHP error log for the exact error that occurred during the uninstall attempt. The error log is the most reliable source of truth.
  • As a workaround, you can often successfully delete the plugin by first going to Settings → Autoptimize, disabling all optimization options (CSS, JS, HTML, Images), and saving changes. Then, try deleting the plugin again.

5. Manually Remove the Cache (Last Resort)

If the cache is completely stuck and cannot be cleared from the WordPress admin, you may need to manually delete it.

  1. Access your website's files using an FTP client or your hosting provider's file manager.
  2. Navigate to the wp-content/cache/ directory.
  3. Delete the entire autoptimize folder.

Warning: Only do this if you are comfortable with file management. Ensure you have a recent backup of your site first.

Conclusion

Most Autoptimize cache and 404 errors are resolved by implementing a thorough, multi-layered cache-clearing routine. The key is to remember that Autoptimize operates at the page generation level, and its output is often cached again by other systems. By ensuring all caches are purged in the correct order and that the 404 fallback is active, you can maintain a fast and stable optimized website.

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