Plex refuses to allow a particular artist to exist in library, always retags it as Various Artists

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:

[HowTo] Configure Plex to use embedded metadata (music)