If turning on Airplane mode on your device is the only way you can connect to your camera, or get Live Preview to work with the GoPro App, then your device's APN settings are preventing the GoPro App from working on your device.  There are apps that affect data compression and your device's APN settings, which ends up conflicting with the GoPro App. Some examples of these apps are:

  • Onavo
  • APN-Switch  
  • APN OnOff
  • Snappli

If you have any of these apps, you'll need to uninstall that particular app and restore your APN settings to default, to have the GoPro App work with or without Airplane mode enabled.