In case anyone doesn’t know the Google’s solution:
If your Android device doesn’t appear in Android Device Manager, or if you see Unknown location despite your device being online and running Google Play services version 3.2.25 or higher, follow these steps:
Open Google Settings from your device’s apps menu.
Touch Android Device Manager.
Uncheck Allow remote factory reset.
Go to your device’s main Settings menu, then touch Apps > All < Google Play services.
Touch Clear Data. Note that this action doesn’t remove personal data.
Go back to Google Settings and select Allow remote factory reset.
Restart your device.