We’ll see you in the morning. 
A Scan Library Files will find a movie. Using Get Info would show you where it found it.
But that’s not why I asked you to Scan. Let me explain please.
In your OP you describe three issues.
- server unavailable (i figured unclaimed)
- strangeness in posters and thumbs (indicating maybe permissions, scan/refresh, or repair db)
- certain media unavailable (needs a plex dance or sqlite3 repair or drive failing or?)
We solved (1) and you’re back in control where things work partially. However in the process:
- You struggled to find a Get Info because I wasn’t clear
- Sadly on the Details page, the Get Info is hidden in the horizontal dots menu …
- I wanted you to mouse over a poster on your Home page (or Movies Library View).[1]
What we can do for: (2) Poster weirdness (3) Movies unavailable
- Clarify from you what works and what doesn’t, e.g. all TV shows are fine, some films no.
- Enable debug mode following the directions in this article.
- Get a description of where your media lives in your QNAP filesystem. We need to know folder names and locations, what shares you’ve made. Basic stuff.
- Get logs from the server to double check it’s healthy.[2]
- fsck your drives.
- Reach out for help when we know the above.
Fixing poster and thumbnail weirdness can’t happen until we understand why you see Unavailable for a movie you didn’t delete. It seems like a lot because it is, but you’re doing great. They don’t make QNAPs all that easy to work with, and Plex has it’s quirks.
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Home page posters will show Get Info when you click the vertical dots. ↩︎
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You would reboot the QNAP 451 and give it a full 15min to do whatever it really wants to do, then use the hosted web app and go into Settings → Troubleshooting → Download Logs. Then drop the zip file it gives you into your reply. ↩︎
