Fluctuating orientation measurements are expected when a mobile device's pitch measurement approaches 90°. They are a result of the "Gimbal Lock" phenomenon.
The Gimbal Lock occurs at a singularity point in the orientation measurement configuration: when the pitch of the mobile device is 90°, changes in yaw are indistinguishable from changes in roll, i.e. the orientation is not fully defined. Consequently, azimuth and roll measurements become unstable as the pitch approaches the singularity at 90°.
