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Why Regenerate Thumbnails Fails Silently (And How to Fix It)

19 threads Sep 16, 2025 Plugin → Regenerate thumbnails

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You've clicked the "Regenerate" button, the plugin says it was a success, but your images haven't actually changed. This silent failure is one of the most common and frustrating issues users report with the Regenerate Thumbnails plugin. Based on community reports, here are the most likely causes and how to resolve them.

Why Does This Silent Failure Happen?

The plugin relies on WordPress's core image processing functions. When it reports success but no new files are created, it usually means the process was initiated but was blocked or failed at a deeper level without returning a clear error message to the plugin itself.

Common Solutions to Try

1. Check for a Missing PHP-GD Library

This is a critical underlying requirement. WordPress needs the PHP-GD library (or ImageMagick) to process images. If it's not installed on your server, image generation will fail silently. You may not get an error during upload either. Contact your web host to confirm that the php-gd library is installed and active.

2. Investigate File and Folder Permissions

The plugin needs write permissions to your /wp-content/uploads/ directory to create new image files. If permissions are incorrect, the process can fail without a clear error. Ensure your uploads folder and its subdirectories have the correct write permissions (usually 755 for folders and 644 for files). Your web host can assist with this.

3. Rule Out Conflicting Code

A theme or plugin might be interfering. This is a frequent cause of strange behavior, like generating unexpected thumbnail sizes (e.g., 0x60) or preventing generation entirely.

  • Test with a Default Theme: Temporarily switch to a default WordPress theme like Twenty Twenty-One and try regenerating a single image.
  • Disable All Plugins: Deactivate all plugins except Regenerate Thumbnails. If it works, reactivate them one by one to identify the culprit.

4. Verify Your Custom Image Size Registration

If the plugin works for some sizes but not your custom ones, the issue is likely in your theme's functions.php file. The Regenerate Thumbnails plugin can only generate sizes that are currently registered by your theme or plugins.

  • Ensure your add_image_size() calls are not wrapped in conditional logic that might prevent them from running when the regeneration happens.
  • Make sure they are registered early enough in the WordPress process, typically hooked into after_setup_theme.

5. Consider Extremely Large Source Images

While the plugin can handle large files, server memory limits can sometimes be exceeded by images with very high resolutions (e.g., 10,000x7,000px), causing a silent failure. Try scaling down a problematic image to a more manageable size (e.g., 2500px on the longest side) and re-uploading it.

6. Try an Alternative: WP-CLI

If you have command-line access to your server, using the WordPress CLI tool can often bypass issues that block the web-based plugin. The command is straightforward:

wp media regenerate

What to Do If You Still See 404 Errors

If images return a 404 error after regeneration, it's possible the new files have slightly different dimensions (e.g., 1024x804 instead of 1024x803). If the "delete old thumbnails" option was enabled, the old file was deleted, and any hardcoded references to it in posts will break. Regenerating again may not fix links in existing content.

By methodically working through these common causes, you can usually identify and resolve the reason behind a silent regeneration failure.

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