It is Polylang, which I installed just as I deactivated Folders. All the images data (caption, description, …) must be translated in the various site’s languages, otherwise they do not appear. The only two photos that I translated where the two which were at the ??root?? of the media library, this is why I was confused and thought that the missing pictures were due to Folders. I hope this clarifies the issue. Thanks again.
