Seemingly at random a number of local files I have uploaded to my computer and downloaded to my android phone grey out on my phone. They are perfectly accessible on my computer, but are greyed out on my phone and unable to be played unless I select them directly. I can still play these songs but they are automatically skipped in the queue and cannot be added to playlists.

I've been having this problem since I started using Spotify and I've been able to remedy it by removing and redownloading files or uninstalling and reinstalling Spotify, but without fail another file will grey out a week later, seemingly at random. I'd like to know if there's a more permanent solution so this isn't something I'm having to constantly remedy.