The “Various” tag came from some albums that I had used EAC (Exact Audio Copy) to fetch the tags. I’ve just made it a habit to use MP3Tag or MusicBrainz Picard to correct and supplement the tags after the CD is initially ripped.
It was sometime ago, but I think it was just one album with “Various” as album artist that caused the glitch, and albums added after that were assigned to another artist. It wasn’t “Ashford and SImpson” for me, but all compilation albums came up with the same artist.
I would move all of the “Various Albums” artist temporarily out of the library, correct the album artist tags, and do the Plex Dance. After that, I’m sure it will work as you expect it to. 
