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Issue and steps to reproduce
When shuffle is engaged in a collaborative playlist, songs will shuffle only between those uploaded by the user associated with the first song to play.
1. Enter a collaborative playlist with multiple songs added by two or more users.
2. Activate shuffle.
3. Click play in the playlist context
4. Click forward to skip tracks. Notice that there is a random element, but only tracks added by one user are being played.
3. Double click a song by a different user from the one in method #1.
4. Click forward to skip tracks. Notice that the tracks being chosen are keyed to that user who added the first track you played.
Macbook Pro 2017
Could you send us your exact Spotify version numbers? Also, does the same happen if you use a different device?
Let's try reinstalling Spotify to see if it helps.
Keep us posted.