Can you provide a screenshot of your tagging tool showing these tags:
- Album Title
- Album Artist
- Track Title
- Artist (artist of each individual track)
- Track Number
- Disc Number
What is the path that the library is pointing to?
A screenshot of the folder structure under that path would also be helpful.
Is Plex configured to prefer the local metadata? If so, this How-To talks about some of the needs and caveats of that option: