Profi cnc in that thread wrote:
"Bad Gyro is a useful message, but it’s a little lacking in what it means.
The initial Gyro calibration happens straight after poweron, before the system warms up…
So try powering on, letting it warm up a bit, then repowering"
https://discuss.ardupilot.org/t/pixhawk-2-1-gyro-and-compass-problem/12936