The thing with external or networked storage: it can happen that a file gets ‘inaccessible’ to plex server.
Either because the USB/ethernet wire is yanked out or
because some external drives or NAS devices spin down the platters of the hard rives and they take too long to spin them back up when a file is requested.
Any file that is marked as ‘unavailable’ gets removed from the library when you empty the trash. Which means it loses all the metadata associated with it. The info, in which ‘collection’ the items is too.
Next time, when the disk is accessible again, the video might get re-added to the library. Maybe even without you noticing it.
You only notice that all metadata art reset to the defaults.
