Since late last year, users have reported that when they are listening to Spotify and an ad appears in the Now Playing section, Spotify sometimes freezes. The ad doesn't play, but neither does the music. Reloading the page sometimes starts the music playing again, but not always.
The issue has been reported by users of Adblock Plus and uBlock Origin as well as AdBlock, in both Chrome and Firefox. That tells us the problem is on Spotify's side, not a bug in the ad blockers.
Our developers have been looking into this issue. We believe it's caused by Spotify's failure to recover gracefully after an audio ad is blocked multiple times (somewhere between two and six). We have a lead on a solution, which we're continuing to investigate.
To get your music to play again, first try reloading the page a few times. If that doesn't work (it probably won't, in fact), return to https://open.spotify.com/browse/featured and select the playlist or album again.