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Why Regenerate Thumbnails Gets Stuck and How to Fix It

33 threads Sep 9, 2025 Plugin → Regenerate thumbnails

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If you've ever tried to use the Regenerate Thumbnails plugin only to have it freeze at a certain percentage, you're not alone. This is a common issue reported by many users. This guide will walk you through the most likely causes and provide step-by-step solutions to get your thumbnails regenerating smoothly.

Why Does the Process Get Stuck?

The regeneration process is a resource-intensive task. It works by processing your media attachments one by one. If it halts at a specific point, it's often because it has encountered a problematic file or a server limitation that prevents it from continuing. Based on community reports, getting stuck at percentages like 47% or 71% is frequently tied to a single, specific attachment that the plugin cannot process correctly.

Common Solutions to Try First

1. Check Your Browser's Console for Errors

Often, the most direct clue about what's going wrong can be found in your browser's web console. An error here can point to a specific failing image or a server communication problem.

  • In Chrome: Right-click on the page, select Inspect, and then click on the Console tab.
  • In Firefox: Click the menu button (☰), select More Tools > Web Developer Tools, and then click on the Console tab.

Look for any red error messages that appear when the process freezes. These messages can be invaluable for diagnosing the issue.

2. Increase Your PHP Memory Limit

Image processing requires a significant amount of server memory. If your PHP memory limit is too low, the process can fail. A common fix reported by users is to increase this limit by adding the following line to your wp-config.php file:

define( 'WP_MEMORY_LIMIT', '256M' );

You can start with 256M and increase it to 512M or 1024M if necessary. Always remember to make a backup before editing core WordPress files.

3. Clear Your Browser Cookies and Cache

Authentication issues can sometimes cause the process to halt. A simple fix is to clear your browser's cookies and cache for your site, or simply log out of WordPress and log back in. Trying a different web browser entirely is also a good troubleshooting step.

Advanced Troubleshooting Steps

4. Identify a Problematic Attachment

If the process consistently fails at the same percentage, a specific attachment is likely the culprit. The Regenerate Thumbnails plugin attempts to process all attachments, including files like PDFs that cannot have thumbnails. To test this theory, try regenerating thumbnails for only featured images. If that works, it confirms a non-featured attachment is causing the problem. Unfortunately, the plugin's interface does not provide a log to identify the exact file, so further investigation is needed.

5. Check Your Server's PHP Error Log

Your server's PHP error log often contains more detailed error information than the browser console. Contact your web host for instructions on how to access this log. Look for errors that occurred at the exact time you attempted the regeneration; these can pinpoint fatal errors related to specific images or server limitations.

6. Check for Plugin Conflicts

Other plugins, particularly those that also interact with images (like Smush It or other optimization plugins), can sometimes interfere with the regeneration process. As a test, temporarily disable all other plugins and try regenerating again. If it works, reactivate your plugins one by one to identify the one causing the conflict.

7. Verify Image Library Support

WordPress requires either the GD or ImageMagick library to be installed on your server to resize images. If neither is available, the plugin will not be able to create thumbnails. You can check this by uploading a new image; if no thumbnails are created for it, you have a server configuration issue and should contact your host.

What to Do For Very Large Sites

If you have thousands of images, the browser-based regeneration method may be impractical due to browser timeouts or server limits. For large sites, the recommended solution is to use WP-CLI, a command-line tool for WordPress. This method processes images directly on the server, eliminating browser and HTTP request timeouts. The command is:

wp media regenerate

You will need command-line (SSH) access to your server to use this tool.

Important Final Notes

  • Always Backup: Before performing any bulk operation like this, ensure you have a complete backup of your site and database.
  • Be Patient: Regenerating a large library can take many hours. Keep your browser tab open and avoid putting your computer to sleep.
  • The Regenerate Thumbnails plugin uses WordPress's built-in image processing functions. It does not automatically run; it only processes images when you manually initiate it from the Tools menu.

By methodically working through these steps, you should be able to identify and overcome the hurdle that's preventing your thumbnails from regenerating.

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