While I'm not sure why this specific song is missing, I know that most of the times that Spotify removes certain music is related to legal and ownership issues. Sometimes, artists and/or some of their music can temporarily be removed while Spotify is in the midst of making an agreement with artists and recording labels. If it isn't back soon, you can fill outthis form to tell Spotify that it should be added to their library. Hope it's back soon!
Let me know if there's anything I can help with! :) . If I help you, click the "Accept as Solution" button to help share the solution with others. . Kudos are never expected, but always appreciated.