Force quit might be needed when using Pix4Dcapture:
Force quit any other app that could be in conflict with Pix4Dcapture when connecting to the drone.
1. Open the Settings app on the Android device.
2. Scroll the list and tap Apps, Applications or Manage apps.
3. (optional) On certain devices like Samsung, tap Application Manager.
4. Scroll the list to find the app to force quit.
5. Tap FORCE STOP.