Yesterday i had to fly at a wind power generator. First fly went good, but during the second I had NO SIGNAL on the GO app. I thought i lost control, but I could land manually. Switching on, off, changing batterys and restarting the tablet did not fix it. When I looked through the menues of the app i found a message about the compass. .. There was something metall and it need to be calibrated again. .. I did it and everything was fine. Any idea what happens ?