There are a few cases when the images are automatically compressed:
- By default, the “Optimize media on upload” option is switched on in your ShortPixel settings (Settings > ShortPixel > Processing). If you don’t turn it off, the images will be compressed automatically after they are uploaded to the Media Library.
- Some plugins (like thumbnail regeneration or thumbnail editor plugins) can change or remove the WordPress metadata and trigger the re-optimization. For more information: Why are my images re-compressed?
- The Bulk Optimization process (Media > Bulk ShortPixel) was already started and a list of images was sent to be processed.