How to empty ShortPixel cache?

I previewed a page that references images that I hadn’t uploaded yet.
Now, after uploading the images, they still are not displayed.
It looks like the ShortPixel cache remembers that the initial image retrieval failed and cached the absence of the image.
Is there a way to force a refresh of the ShortPixel cache (preferably for the affected images only) ?

Note: Emptying the Autoptimize cache didn’t help (I didn’t expect it to).