Roman, thank's for sharing your experiences with this issue. One suggestions: you could install an app which displays the sensor values and check values of the accelerometer, the gyroscope and the compass. Maybe the compass is not really the problem on your iPhone6 but a different sensor.
over 4 years ago
Yes, the different iPhone is on iOS 8.3, mine on 8.2. But: I have just now fixed it on my iOS 8.2 device as well. Here is what I did: