When you listen to 60 songs from a shuffled playlist of 300 songs, the likelihood of hearing the same song 3 or more times is approximately 29%. (Quick simulation: https://play.golang.org/p/2RNADWRQx4h)

This is related to the Birthday Paradox.

EDIT: Disregard this. I was thinking of shuffling as repeatedly choosing songs uniformly at random with replacement from the playlist, but commenters reminded me that shuffling shouldn't work that way. I found an open issue about this: https://community.spotify.com/t5/Desktop-Mac/Shuffle-should-...: "In a playlist of mine that is more than 6 hours long, shuffle often plays songs twice or three times within 30 minutes."