Having problem calibrating IMU in Phantom 3 Pro. Finally had a nice day to fly but GO app said to calibrate IMU. When I got into calibration menu none of the boxes had any numbers showing. Clicking Check IMU and Calibrate IMU did nothing. Even waited until the Phantom's battery reached 50%. Phantom flew without problems last time and I had no crashes. Followed all the procedures: Fully charged batteries, cool bird and battery, level surface away from any magnetic material. Any ideas?