Extended ASCII letters (those with diacritic or “accent” marks) can be problematic on some servers, so WP normally removes all diacritics in uploaded file names. So I’m unsure how you have file names like kyn?.png. Should have been converted to kyna.png. Does the file’s URL that the page is trying to load have diacritics in the name? You can check all requested URLs for a page in your browser’s network developer tool. If the requested URL has diacritics to match the file names, then the issue is with the server itself.
If the requested URL has no diacritics but the file names do, we need to check the source data to see if it’s correct, as WP may have stripped the diacritics between getting the data and making the request. Determine the ID of an image’s attachment post. In the media library, check the edit link for one of the problem images. The ID is the integer after the “post” query var.
Get into the phpMyAdmin app, usually through your hosting account. Locate the WP DB in the app and click on the postmeta table. In the search tab for the table, search for the post_id we’ve determined. It should find a record keyed _wp_attached_file. Does the filename there have diacritics or not? If so, there is possibly a relatively simple solution to prevent WP from stripping these.
But if there’s a fundamental mismatch between this data and the file names on the server, I fear you’ll need some sort of custom script to rename all the files to match the stored data.
