To reproduce:

1. Download attached project "SafariView Repro.zip" and open in Unity
2. Open "SampleScene" scene
3. Build for iOS
4. Deploy the Xcode project to iOS Device
5. Press the "Set landscape left" button
6. Press the "Set landscape right" button
7. Press the "Launch SafariView" button

Expected results: SafariView stays on Safari and did not return to Unity
Actual results: SafariView returns immediately to Unity the first time it is used after setting Screen.autorotateToLandscapeX properties

Notes:
- Could not check on Android, because Plugin was made for iOS platform

Tested with:
- iPhone 7 Plus, iOS: 12.0 - Reproduced
- iPhone X, iOS: 11.3.1 - Reproduced

Reproduced on Unity 2018.3.0f1, 2018.3.7f1, 2019.1.0b5 and 2019.2.0a6
Not reproduced on Unity 2018.2.20f1 and 2018.3.0b11
Regression on Unity 2018.3.0f1