This keeps happening to me. I will be listening to a playlist with over 300 songs, and it will be on shuffle. Then all of a sudden, the next song will be some weird techno song I have never heard of before and it will stay on that techno playlist until I switch it or stop it. This even happened to me once in the middle of the night when my PC was on and connected to Spotify. There was no music playing, and then all of a sudden it started to play that music.