We’ll see. In the mean time I’ll just run a quick find/replace job in the sqlite db on these Muppets entries 
edit: for those that want to know:
- get the app “DB Browser For SQLite”
- close Plex Media Server
- open the database file (make a backup first obv) in the folder /Plug-in Support/Databases/com.plexapp.plugins.library.db
- select Browse Data, table “metadata_items”
- filter to metadata_type 8 (=Artists), filter title/title_sort on “Various Artists/Various Artists”, write down this id. This is the correct “various artists” id you’ll apply to all the wrongly scanned albums. Say this is 12345
- in the same way, find the id of the wrong album artist that Plex applied to all your compilations, say it’s 23456. You’ll notice btw that the “title” and “title_sort” fields are not the same! In my case this was “The Muppets”/“Various Artists”, but it could be anything.
- clear all filters, then filter for metadata_type 9 (=albums) and filter parent_id for 23456 (i.e. the wrong artist id)
- in each line, replace parent_id 23456 with 12345
- file → write changes
- start Plex Media Server
Looking at this, it seems that the source of the bug in the Plex Music scanner is that when it encounters a V/A compilation album (ie, no Album Artist) it looks up and applies the id of the first match returned against a query for “Various Artists” in the “title_sort” field, while it should look up/apply the id of the first match where “title” and “title_sort” fields are “Various Artists”.
