Do generated thumbnails expire?

I’m using a CDN in pull configuration to serve images (resized to different dimensions) that started returning a high number of 404 recently. I went to check on the server and a bunch of resized thumbnails that I’m pretty sure were there are now not physically present on the server.

In a regular setup where I serve the images myself this wouldn’t be an issue as Kirby would just resize them again on the fly, but in this case the CDN can’t find them on the origin and it’s causing things to break unexpectedly.

This might sound totally weird but I’d rather get a confirmed negative answer to rule it out, is there a kind of garbage collection or expiry that happens to generated thumbnails?

The thumbs URL changes if a page is renamed or a file modified, but then the pull zone should correctly fetch them. Other than that, thumbs shouldn’t get deleted, at least not as far as I know.