Fixing the 'rewrites_cached' Error in Converter for Media: A Complete Troubleshooting Guide

If you're using the Converter for Media – Optimize images | Convert WebP & AVIF plugin and encountering the rewrites_cached error, you're not alone. This is a common server configuration issue that prevents the plugin from dynamically serving WebP/AVIF images. This guide will explain what causes this error and provide the most effective solutions to resolve it.

What Does the 'rewrites_cached' Error Mean?

This error occurs when your server or a connected service caches HTTP redirects. The plugin works by dynamically redirecting image requests (e.g., image.jpg) to their optimized versions (e.g., image.jpg.webp) based on the browser's Accept header, which indicates supported formats.

The problem arises when the server's cache stores the result of the first redirect instead of processing the rewrite rules from the .htaccess file or Nginx configuration on every request. This means all subsequent visitors get the same image format (e.g., WebP), regardless of whether their browser supports it.

Common Causes and Their Solutions

1. Server-Level Caching or HTTP Reverse Proxy

Many hosting providers implement server-level caching mechanisms or reverse proxies (like Varnish) that can interfere.

• Solution: Contact your hosting support and explain the issue. Provide them with the exact error message from the plugin. Request that they disable HTTP caching for image requests or ensure the cache respects the Vary: Accept header.

2. Content Delivery Networks (CDNs)

CDNs like Cloudflare, QUIC.cloud, or others are frequent culprits. They are designed to cache content at the edge, which can break the dynamic image redirection.

• Solution for Cloudflare: Try enabling "Developer Mode" to bypass the cache temporarily. For a permanent fix, you may need to adjust Cloudflare's Page Rules to not cache images or to properly respect the Vary header. Note that some Cloudflare plans have limited support for the Vary header.
• Solution for QUIC.cloud (LiteSpeed): Users have reported that disabling the QUIC.cloud CDN resolves the error. If you must use a CDN, you may need to configure it to exclude image paths from caching, though this can be complex.

3. Caching Plugins (WP Rocket, LiteSpeed Cache)

While the error is primarily server-related, caching plugins can sometimes contribute to the problem or have conflicting settings.

• Solution: As a diagnostic step, temporarily disable all caching plugins. If the error disappears, you know the issue is related to caching. You can then reactivate the plugin and work on configuring it to exclude image redirects from being cached. Consult your caching plugin's documentation for how to set exclusion rules.

4. Nginx Server Configuration

Since Nginx does not use .htaccess files, the plugin provides custom configuration snippets that must be manually added to your server's main Nginx configuration file.

• Solution: Ensure you have correctly added the configuration rules provided by the plugin in the Help Center tab. This is not a one-time task; if your server or hosting management panel (like RunCloud) updates the Nginx config, your changes might be overwritten. You may need to re-apply them or work with your host to make them permanent.

5. Incorrect Cache-Control Headers

As noted in community discussions, the plugin sets Cache-Control: private to try and prevent public caching of the redirects. However, some users suggest that using a Vary: Accept header is a more standards-compliant method for informing caches that the response varies based on the Accept header.

• Advanced Solution: For users comfortable with code, there is a filter hook (webpc_htaccess_mod_headers) that can be used to modify the headers being set. However, this requires custom development knowledge.

Diagnostic Steps

1. Check the Help Center: The plugin's settings include a "Help Center" tab with vital information, including your server configuration and specific instructions. Providing a screenshot of this tab is often the first step recommended for troubleshooting.
2. Isolate the Problem: Disable all caching layers one by one (CDN, server cache, WordPress plugins) to identify which component is causing the conflict. Reactivate them one by one after the error is resolved to find a compatible configuration.
3. Test Thoroughly: Use browser developer tools (Network tab) to check the headers on your image requests. Look for the Vary header and confirm that images are being served in different formats (WebP, AVIF, original) to different browsers.

Important Note

It is a common misconception that simply disabling all caching is the ultimate solution. While it may resolve the rewrites_cached error, it can negatively impact site performance. The goal is not to eliminate caching but to configure it correctly so that it works in harmony with the image conversion plugin. This almost always requires coordination with your hosting provider or CDN support team.