I am on Windows 7, desktop version. I have had the "This song is not available. If you have the file on your computer you can import it" issue for about half a year now. I was using the bandaid fix of downloading an older client every day, as it Spotify would automatically update when I turned my computer off.
Now, Spotify is automatically closing my client and updating to the newest version (that I can't play ANY songs on).
Spotify is now completely unusable for me for more than a minute or two.