Spotify's shuffling is most certainly not random. Every once in a while I get a bug where it simply shuffles through various songs from 4-5 albums and will neve

Spotify's shuffling is most certainly not random. Every once in a while I get a bug where it simply shuffles through various songs from 4-5 albums and will never pick songs outside that set. Restarting the app corrects the behaviour. To me that's some level of proof, because the songs are all there. So what's the algorithm really doing?