Actually it was not a case where the site was cloned, but rather RTE content was copied from your old site to another. We don’t currently re-upload images when they are pasted so the image still was pointed to the old site. The old site then was deleted, deleting the image being referenced on the new site in the process.
For now I recommend re-uploading images in the rich text fields/elements. If you're copy-pasting content from an external website it's easy to check the code of the site and see if it's referencing images from different servers. It's hard to tell though if an image is being referenced to another webflow site since they would look the same (using the cloudfront url).