This happened to me a couple weeks back. I updated Unraid to 6.12.13 and Binhex-plex just stopped being able to see itself as a server. I've been able to make it "reappear" by deleting everything from appdata and reinstalling the container, but then it will not let me claim the server, and then it disappears.
I've resolved to running Jellyfin in the meantime, but I did like Plex more when it did work.