Can't play a song I own without Apple Music subscription

I recently upgraded to an iPhone 6 from an iPhone 4. Today I was playing music on my iPhone that I have purchased through iTunes and everything was fine until I got to one particular song. Whenever I try to play the song, I get a message saying that my Apple Music subscription is expired and I need to turn it on in order to stream this song. I get the same exact message when I try to download the song to play offline on my iPhone. The song plays just fine on my MacBook. I have not run into this issue with any other songs, so I'm perplexed as to why I can't play this one particular song.

Has anyone else run into a similar issue? I bought this song over two years ago on iTunes and I'm a bit frustrated that I can no longer play it on my phone. I also have no interest in purchasing the Apple Music subscription - I just want to play the music I already own!

Is this something on Apple's end or is this something I'm misunderstanding about how Apple Music works?