The solution to the Plex issue is simple: check file permissions for the media files and then re-start Plex itself.
Unfortunately it wasn't that simple. The permissions were fine, the
folder and naming convention was fine... for some reason the plex docker
in unraid just wasn't working anymore.
I removed the docker and all plex config/cache files and installed the
official plex docker.. same results... heck even people at plex couldn't
work out what was going wrong.
I was wasting more time than I wanted to so I spun up a vm with ubuntu
server, installed plex, mounted the media shares on unraid via nfs, and
in about 30 minutes the new server had downloaded all the metadata with
cover images...
Don't know what went wrong with unraid..
--- MagickaBBS v0.12alpha (Linux/armv7l)
* Origin: Fusion ~ MagickaBBS (21:4/132.1)