Reproduction step:
1. Open the attached "AccelerometerTestProject02"(04/01/2017) project.
2. Build and run it for iOS device.
3. Hold the device in portrait.
4. Tilt a device to the left a little bit.
- Accelerometer input number gets negative.
5. Hold the device in portrait.
6. Press the button below to start the Ad.
7. Watch the Ad in landscape.
8. When the Ad is done, keep the device in landscape mode and close the Ad.
9. Turn the device back to portrait.
10. See that the input is now reversed.

Notes:
- May be caused by a different device orientation at the start of the ad compared to at the end of the Ad.
- May be related to case 796649 and case 806599
- Screenshots attached.

Workaround:
- Use video orientation according to the orientation of the device setting in the Unity Ad options.

Reproduced with:
5.5.0b1, 5.6.0f3, 2017.1.0a6
iPhone iOS 10.2.1