Thanks for replying. I tried creating and renaming a 0 byte file. Still 0 bytes. A small test file did not get corrupted. I think I won't spend much more of my time, or yours, debugging this. The movies can be redownloaded so I didn't really lose anything critical. The NAS is over a decade old and ...

I renamed all my movies and tv shows - all .mkv files - to a jellyfin structure and after renaming the movies are now unplayable. The TV shows still play for some reason. Files are located on a Seagate Personal Cloud NAS shared to windows with SMB Renamed the files using format: {drive}/{jellyfin.id ...