Song Unavailable on iPhone?

[SilverContrails]

So I have Spotify Premium and I've made a playlist of mostly Local Files to listen to while I'm driving. I have the whole thing downloaded and it works great. At some point I realized there was one song from my local files that wouldn't play, and upon checking the playlist on my phone I realized it wasn't there at all. So I got on my computer and tried to add the song to my playlist again but it said it was already there, and sure enough when I checked the playlist on my computer it was there. I tried redownloading my playlist to my phone and while it was downloading the song showed up for a brief moment before disappearing again. I then tried removing the song from my playlist on my computer and readding it and the same thing happened. I haven't moved the file since adding it, and the song plays just fine on my computer, but whenever I try to switch between playing the song on my computer to my iPhone, it says the song is unavailable. No other song on my playlist does this, it's just the one. What's going on here?