First I had the issue that i couldn´t listen to some songs in my own Playlist.
The song I clicked on my own playlist, just got skipped, but if i search for the song again and click on it (in the search results, not in my playlist) i could hear the song with no Problems.
Then i saw that the cover had changed, so in my playlist the song had an old cover and in the search results there was the same song, with a new one.
So I added the song again to my Playlist, clicked on it and i could listen to it with no Problems.
Maybe thats the Issue, that if the cover gets updated and you have the song in your playlist with the old cover, it is bugged and you can´t listen to it.
Hope my Post Helps.
Some additional info: I´m Using Windows 10 but i dont think it has anything to do with that, because a friend of mine had the same issue and he has Windows 8.1.
As stathis125 says, it can occur that a track is updated (removed, and an updated version added) and thus its source changes.
Not so much a bug, as probably just a minor annoyance.
Sometimes songs' unique url has to change.
I think that 's what happened here. They made a new url for the song and you had to add it again.