I've had this issue recently where when I either shuffle through an artist's music, or start a radio based on an artist, it will only choose songs that I frequently listen to on a normal basis.
For example, I might listen to one album by a certain artist somewhat frequently. But, when I want to shuffle everything by that artist, it is 90% the songs on that particular album. If I wanted to just listen to that album, I would pick that album.
Similar thing is happening when I start an artist radio. When I start an artist radio, I want to listen to their music PLUS music that is similar to them. Instead, Spotify is just picking songs that are related to my most popular playlists, whether or not it is similar to the artist that I chose to start the radio from.
I like to find new music to listen to, and these are normally both options are ways in which I find new music that I like. It's trying to play music that it knows that I like, but now it's doing it so much so that it's faulty.