Reset the location of the location that the Google Play Music Manager uploads music from.
1.Click the Google Play Music Manager icon in your system tray at the bottom right of your screen (Windows), menu bar in the upper right corner (Mac) or notifications area (Linux) to access the Google Play Music Manager.
2.Select the ’Advanced’
3.Click ’Change’ and select your preferred location
By doing this and restarting the application, it will upload everything it missed the first time around.