I'm on desktop, windows 10. I updated my Spotify a moment ago, but after the update the Spotify app stopped outputting sound. The songs were showing that they were playing, but the sound was not coming through anywhere. If I double-clicked on my playlist, it would start playing the first song, but that was a one-time fix, the next time I clicked on that playlist, it would stop outputting sound like every other song. So to sum everything up, Spotify was playing songs, but the sound kinda disappeared, my PC was not receiving any sound at all from the Spotify app.
I also have Spotify app on my phone, Samsung Galaxy S5 Mini. I don't use my phone at all, I only have it for work/business purposes. The sole reason why I installed this app on my phone was to fix a previous bug. The previous bug was that the PC version of Spotify was stuttering in the beginning, whenever I opened any song on desktop app, the song would stutter heavily for 3-5 seconds in the beginning, then it would continue playing normally. This whole stuttering issue got fixed when I installed Spotify on my phone for the first time. Was very weird.
Now we have a 2nd issue, the current one. After the most recent update, Spotify lost sound on the desktop app. I checked my phone again, updated the app on the phone as well and it magically fixed itself on desktop. Hope this helps someone.