Hi there !
I have exactly the same problem ! (Synology DS414)
When i refresh all metadata, everything is ok, but when i make modification (add/remove movie …) and if i click on another movie, plex re download metadata… exactly same as Storm_ryder screenshots.
Metadata seems to be still there (posters), but plex need to redownload all metadata of the movie…
Did you find the issue ?
Thx