We're aware that for some devices a restart is required when swiching audio devices while playing back music.
We're not able to provide an exact timeline for a fix, but we really appreciate you letting us know about this. We're always working to make Spotify a better experience. We'd recommend keeping an eye out for updates to the app.
This happens to me all the time. Seems to be when I'm using bluetooth headphones and they sleep after not playing for some time, when I pick them back up and start playing again, I get the "Can't play the current song." Restarting the app always works, but it is *super* annoying.