Enabling Bluetooth and GPS
Say your GCG scan progress bar is not moving at all or moving slowly through the entire day. The obvious thing to check is if you have Bluetooth and GPS enabled all the time. If either of them are not turned on, contact data will not be collected. You will see a "Scanning Stopped" the notification panel of your phone, and a banner "Please enable GPS/Bluetooth" at the bottom of the App. If so, you should enable Bluetooth and GPS. Here is a video on how you can do it.
In rare cases, if you denied permission for GCG to use Bluetooth when the App prompted you, and you selected "Don't ask again", just keeping Bluetooth on will not be sufficient. You need to go to Android Settings, you App Manager, select GoCoronaGo, and under permissions, enable Location permission.