Iv'e had spotify for years while using the local files feature to listen to my favorite songs that aren't on spotify. However, for some reason when I recently tried to add a new song via the local files, when synced to my IOS device it won't play on my iphone. It shows up on my iphone, its downloaded, but when I tap on the song to play it on my iphone it turns green like its playing for a fraction of a second, but then immediately deselects the song and doesn't play anything. What is even weirder is it will play fine on the desktop app. 

I tried uninstalling the IOS app, but that only hid all my other local songs on my playlist and i can no longer access them on my iphone. I'm not worried about adding them back as i have them all on a folder on my pc, but I still cant play any of them if I re-add them. Ive tried using different wifi's to try and sync them, but i don't think syncing is the problem. Any help is much appreciated.