Responsive images - Media folder - some images not resized

Hi. I’m concerned there is something going wrong.

I used the Total Validator app to create all the images, in the media folder: responsive sizes and webp formats (Create all thumbnails in one go (not on fly)?). I can see that all the images were created at the same time.

But the handful of original images copied into the media folder that have not been resized were created at different later times. Which suggests a visitors browser was calling these images and ignoring the Kirby thumbs?

What’s strange is that this might just be one or two images on a page that has ten images.

Sorting the files into date order, the first nine images have been created at a different time and are unsized, original, large, files:

I’ve just looked at the visitor analytics. It reports that no one has visited the two pages, since the 9 June, that have the original images in the media folder. Which if true leads to the question, what event is occurring for these original images to be copied into the media folder? A bot crawling around?