If Plex Media Server can’t find items in a library, what can one reasonably do?

My Movies library — which I re-created a couple weeks ago — constantly fails to find new files, and forgets tens of files that it previously knew about.

Every one of these goddamn papercuts pushes me ever-closer to Jellyfin. And I hate that for me.

(Please, I’m not interested in alternatives. Just fix my Plex Media Server. It’s very sick.)