"Invalid response from server", what is this?

The error message "Invalid response from server" can be sometimes puzzling, especially when the actual image exists and looks good when viewed in a browser.

Check the response output

If you receive this error, it might be that there is some output from another plugin (or some notice/warning) that corrupts the JSON answers of the AJAX calls of our plugin. To see this output, do the following

  1. Go to Media > Bulk ShortPixel
  2. Start optimizing your images (if you didn't do it yet)
  3. Open the Developer Tools of your browser (usually F12 on Windows, or Cmd-Opt-' on Mac)

Do as the screenshot shows:

  1. Click on the Network tab
  2. Select the XHR filter
  3. Click on any admin-ajax.php?_fs_blog_admin=true request
  4. Select the Response tab. What you see on the screenshot is the correct AJAX call.

If you don't see something similar, then we recommend you to try to find the conflicting plugin:

  1. Deactivate all plugins except ShortPixel
  2. Activate one by one the plugins. After each single activation, retry the bulk optimization until you find the plugin that corrupts the JSON responses.

Check if your server gets overloaded

If the above did not help, it is possible that your server has limited capacities in terms of processing power and memory. Some of ShortPixel's features may use more resources than others, so it can happen that the server gets overloaded. You can try temporarily disabling the following features.

  • Convert PNG images to JPEG
  • Optimize Retina images
  • Optimize other thumbs

If you have many thumbnails, you can try excluding some of them from optimization, since each thumbnail (and its WebP + AVIF counterpart) adds up to the server load. To know how to do this, check this article: How can I optimize only certain thumbnail sizes?

For more information, check this article: My website seems to be slower, could this be because of ShortPixel Image Optimizer?

Other common issues

If you still cannot find out what's happening, please have a look at Why some of the images and/or thumbnails cannot be optimized?

If the error is happening for all your images and you cannot optimize anything, please have a look at the following article and make sure all is in order: None of my images were optimized, why is that?

Contact your hosting provider

As a last resort, we recommend you to contact your hosting provider in order to know why our plugin cannot access your images.

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