To reproduce:
1. Open users attached project "Bug auto rotation.zip"
2. Open "scene.unity" scene
3. Build for iOS
4. Deploy the project to an iOS device through Xcode
5. Hold the phone in portrait mode (1.png)
6. Check Landscape box (2.png) observe as Device orientation is Portrait and Screen orientation is Landscape (correct)
7. Uncheck the Landscape box (3.png) observe as Device orientation - Portrait (correct) but Screen orientation is PortraitUpsideDown(incorrect)
8. Rotate the device to be upside down and observe as Device orientation is correct but Screen orientation is Portrait (incorrect) (4.png)
9. Check Landscape box (5.png)
10. Unckeck the Landscape box (6.png) and observe as the Screen and Device orientation is correct now
11. Rotate the device back to Portrait mode (7.png), orientations are still correct
12. Checking the Landscape box again reproduces the issue again

Expected result: changing screen orientation using Screen.autorotateToPortrait from Landscape to Portrait, Screen.Orientation returns Portrait value
Actual result: after first time changing to Landscape then back to Portrait Screen.Orientation returns UpsideDown for the first time.

Reproduced on:
2017.1.5f1 2017.4.11f1 2018.1.9f2 2018.2.8f1 2018.3.0b1

Device reproduced on:
iPhone 7 Plus iOS 11.1.1

Doesn't seem to reproduce on Xiaomi Mi Note Pro