If you ever have some songs unable to play on the Google Play app, try the following:
- Go into settings -> apps -> all -> MediaStorage -> clear data (This doesn’t delete any of your files, just the cache database with a list of where all the media files are on your phone
- Then reset your phone, so it will rebuild some of the cache again
I downloaded some songs to my phone, then uploaded them to Google Play. I then deleted the local files, and tried to play them with Google Play without success. The system was still trying to play the local versions which didn’t exist. When the cache was deleted, all worked fine instantly!