Long hexa-decimal filenames in iCloud Photos.

You should not be seeing the internal filenames in Photos, unless you are looking inside the Photos Library package. The photo editing extensions are not seeing the original filenames, however, only the internal filenames. You may also be seeing the internal filenames, after a library repair. Sometimes Photos will recover lost and found files after a repair, files that have lost the connection to the thumbnails. These recovered files will then be showing the internal filename. Or some old images shared to Shared albums. Recently shared photos are keeping their original filenames in shared albums.

Newer Photos versions use internally those long gibberish filenames (AFAIK because they are needed for Photos iCloud databases or something like that). They should be converted to the original names when exporting (although for some weird reason .jpg suffix is changed to .jpeg). But that does not happen in some workflows.