Why will some MP3 files refuse to sync offline?

[christophernyck]

I recently upgraded to the new iPhone 7 Plus, and restored my apps from the previous iPhone 6, including Spotify. 

Most everything is working, however, a few of my local files refuse to sync. They are all in MP3 format. My iPhone is on the same Wifi network as my iMac which stores the original files. They play fine on my iMac, but when I try to play on my iPhone it says "Song Not Downloaded." 

I see that some people who have had a similar problem had to uninstall Spotify, reinstall it, and then re-sync everything. I really don't want to have to do this if there's an easier fix. The whole thing makes no sense.

Any help is appreciated. This is maddening.

Chris