How to Fix 'An Unexpected Response Was Received' in WP-Optimize

If you're using the 'WP-Optimize – Cache, Compress images, Minify & Clean database to boost page speed & performance' plugin, you might have encountered the frustrating "An unexpected response was received" error. This message can appear in various parts of the plugin, such as when trying to preload the cache, optimize the database, or compress images.

This guide will walk you through the most common causes and proven solutions to resolve this error.

What Does the Error Mean?

This generic error message typically indicates a communication problem between your browser and the server while the plugin is attempting to perform a task. The root cause can be anything from a simple plugin conflict to a server configuration issue.

Common Solutions for "An Unexpected Response Was Received"

1. Check Your Browser's JavaScript Console

The first and most crucial step is to check your browser's developer console for any specific JavaScript errors that occur when the message appears. These errors often provide the exact clue needed to diagnose the problem.

• How to check: Right-click on the webpage and select "Inspect". Navigate to the "Console" tab. Reproduce the error by clicking the button that caused it (e.g., "Preload" or "Optimize") and look for any red error messages in the console. You can find a detailed guide on how to open developer tools here.
• What to do: If you see errors, note them down. Common errors include "Uncaught SyntaxError" or references to specific scripts failing to load.

2. Investigate Your Server's PHP Error Logs

If the browser console is clear, the issue might be happening on the server-side. Your server's PHP error log will contain detailed records of any problems PHP encountered while executing the plugin's code.

• How to find them: Error logs are often located in your site's root directory (public_html/error_log) or in the wp-admin/ folder. Your web hosting provider can also help you locate them if you are unsure.
• What to do: Reproduce the error, then immediately check the logs. Look for any entries that correspond to the time you triggered the action. You can use a service like Pastebin.com to share log excerpts if you need help interpreting them (remember to redact any sensitive information like your site's URL first).

3. Perform a Plugin Conflict Test

This is one of the most effective ways to identify the source of the problem. A conflict with another plugin is a very common cause.

• How to do it:
  1. Deactivate all other plugins except for WP-Optimize.
  2. Test if the "unexpected response" error still occurs.
  3. If the error is gone, reactivate your other plugins one by one, testing after each activation, until the error returns. The last plugin you activated is the one causing the conflict.
• Note: As seen in the sample threads, conflicts with plugins like MonsterInsights and TranslatePress have been known to cause this specific error.

4. For Preload Errors: Try Running It Again

Specifically for the preload feature, the "WP-Optimize – Cache, Compress images, Minify & Clean database to boost page speed & performance" team has noted that this message can sometimes appear the first time preload is run because it is a long-running task that may cause the browser connection to close prematurely.

• Solution: Simply click the "Run Preload" button a second time. It will often continue and complete successfully on the subsequent attempt.

5. For Minify Errors: Exclude Problematic Files

If the error is related to the minify feature (often accompanied by console errors pointing to a wpo-minify-*.js file), you may need to exclude certain scripts from being processed.

• How to do it: Navigate to WP-Optimize > Minify > Advanced. Find the specific minified file (e.g., wpo-minify-footer-*.min.js) and click "Show information". This will reveal a list of all scripts combined into that file. Click "Exclude" next to any files from third-party plugins or themes, save your settings, and clear the cache to test.

Conclusion

The "An unexpected response was received" error can be stubborn, but it is usually solvable by methodically working through these steps. Start with the browser console and PHP error logs, as they provide the best evidence. If those don't yield answers, a conflict test is your next best bet.