Regenerate Thumbnails is stuck/hanging at X%, how do I fix it?

If the thumbnail regeneration process gets stuck, freezes at a certain percentage, or takes too long to complete, it is usually related to server resource limits or processing too many images at once. You can typically fix this by adjusting the regeneration settings inside ThumbPress.

Solution 1: Reduce the Chunk Size

ThumbPress processes images in batches (chunks). If the chunk size is too high, your server may timeout or slow down during regeneration.

Recommended Fix

Lower the chunk size to a smaller number, such as:

• 5
• 10
• 20

Smaller chunks reduce server load and help the process run more smoothly, especially on shared hosting or large media libraries.

Solution 2: Regenerate in the background

Try the Regenerate in Background option in ThumbPress settings. This allows regeneration to continue gradually in the background instead of processing everything in a single request.

Benefits:

• Prevents browser timeout issues
• Reduces server overload
• More stable for websites with thousands of images

Additional Recommendations

For very large media libraries:

• Avoid running multiple optimization plugins at the same time
• Ensure your server has enough PHP memory
• Use PHP 8.1 or higher if possible
• Temporarily disable heavy cache or security plugins during regeneration

Still Stuck?

If regeneration still hangs after reducing chunk size and enabling background processing:

• Pause the process
• Reload the page
• Start regeneration again

If the issue continues, contact ThumbPress support with:

• Your chunk size setting while regenerating
• Approximate number of images
• Hosting provider
• PHP version
• Screenshot of the stuck progress bar