Can't delete custom labels?

I’ve recently run into this too – it appears this can happen under some circumstances.

There’s a manual fix described in this thread:

short version:

  1. Execute the Plex SQLite app (in the app folder) in the command prompt (power shell, terminal…)
  2. enter .open "<path to database>", pointing to the the com.plexapp.plugins.library.db file in the server data directory (-> Library > Plex Media Server > Plug-in Support > Databases)
  3. enter Delete from Tags where Tags.tag="<name of the tag>" and Tags.tag_type=11; and press return
  4. reload the web app to verify the tag is gone
  5. exit the command shell app by entering .exit and pressing return