Troubleshooting Guide: Why Your WP-Optimize Cache Isn't Working as Expected

WP-Optimize is a powerful tool for caching and performance, but sometimes its caching behavior can be confusing. Based on common community reports, this guide explains why your cache might not be working and how to resolve it.

Common Cache Issues and Their Solutions

1. Specific Pages (Like Homepage) Not Caching

The Problem: You notice that most of your site is cached, but a specific page, often the homepage, consistently shows headers like WPO-Cache-Status: saving to cache and never becomes fully cached.

Why It Happens: This is frequently caused by server or DNS configuration issues. Changes to your Nginx or Apache configuration, SSL setup, or redirect rules (e.g., non-www to www) can interfere with how the caching plugin identifies and serves cached pages.

The Solution:

• First, verify the caching status by following this guide on checking your cache.
• Carefully review your server's configuration files (.htaccess for Apache or Nginx config files) for any rules that might be conflicting with the cache delivery.
• Ensure there are no other caching layers (like server-level Nginx FastCGI cache) that might be serving content before WP-Optimize can.

2. Updated Files (Like PDFs) Still Serving Old Versions

The Problem: After replacing a media file (e.g., a PDF) in your library and clearing the cache, visitors with the old link still see the previous version of the file.

Why It Happens: Browser caching headers can instruct a visitor's browser to store a file for a long time. Simply replacing the file on the server and clearing the server cache may not be enough to force all browsers to download the new version.

The Solution:

• After updating the file, clear your site's cache within WP-Optimize.
• Run the preload function to regenerate the cache.
• As a more robust solution, enable the advanced setting "Always purge this page when saving a post with selected post type" for attachments or the relevant post type.

3. Cache Settings Not Staying Enabled

The Problem: You enable an option like 'Static browser cache headers,' but the setting reverts to disabled after you reload the settings page.

Why It Happens: This almost always occurs because your server is running Nginx instead of Apache. The browser cache header rules are written to an .htaccess file, which is only functional on Apache servers. The plugin detects that the rules are not active and therefore disables the setting.

The Solution: If you use Nginx, you must manually add the equivalent caching header rules to your server's Nginx configuration file. The setting within the plugin will not work for you.

4. Cache Files Not Found in Expected Location

The Problem: You are looking for the static HTML cache files but cannot find them, or you need to configure a custom directory for a containerized environment.

Why It Happens: By default, WP-Optimize stores cache files in wp-content/cache/wpo-cache/. However, this location cannot be customized. Furthermore, the plugin uses dynamically named subdirectories that change when the cache is purged.

The Solution: The cache files are in wp-content/cache/wpo-cache/. For persistent storage in environments like AWS Fargate, you must mount the entire parent wp-content/cache/ directory, as the specific wpo-cache subdirectory path is not configurable and its internal structure changes.

Final Checklist

1. Always clear your cache and run preload after making significant changes.
2. Check your browser's developer tools (Network tab) to see the WPO-Cache-Status header.
3. Confirm your server software (Apache vs. Nginx) and configure it appropriately.
4. Remember that the cache directory structure is dynamic and not user-configurable.

By methodically working through these steps, you can identify and resolve most common caching issues with WP-Optimize.