You may be thinking of this
@JJErrico 's incident
Request advice: Compass error, Yaw error, Weak GPS signal
The conclusion that I came to was that the problem was fixed by doing a compass calibration. BUT, it wasn't due to a flawed calibration because the P4 had not been calibrated for several flights and had not been exhibiting problems. The problems started abruptly and were fixed by a calibration. The other thing to note is that there was no indication from the Go App that a calibration was needed.
There have been other incidents like this. E.g. in this thread
Fly Away
Here it's less compelling that the compass calibration fixed the problem. BUT, it was not due to a flawed calibration as the P4 had many flights without a calibration and no problems.