To reproduce:

1. Download attached "unity_repro_project-min.zip" project and open in Unity
2. Delete everything from Plugins folder except for Facebook SDK Plugin
3. Build for iOS
4. Deploy the Xcode project to the iOS device
5. When App is launched, observe that there is Cube
6. Wait for 3 seconds and in an opened Window press "Continue" button
7. Observe the WebView appear and disappear
8. Wait for 3 seconds again and in an opened Window press "Continue" button
9. Observe the WebView appears successfully

Expected results: WebViews should display correctly regardless of Runtime changes to Auto-Rotation settings
Actual results: WebViews fail once after changes to Auto-Rotation settings

Notes:
- This issue happens only on iOS
- Could not check on Android (Mono and IL2CPP) because Build process always fails
- Could not check on Unity 2018.1 and 2017.4 because Project becomes corrupted
- Could not check on Unity 2019.3 because get Error during the Build process:

"FileNotFoundException: Could not find file "/Users/jonasl/Downloads/case_1169189-unity_repro_project-min/2019.3/Libraries/RegisterMonoModules.h""

- When reproducing this with a Unity Ads, the WebView is never shown and the Application waits forever for the Ad to display, never returning to the App this makes the App lock up
- Workaround: Removing the lines that change the Rotation Settings resolves this Issue

Tested with:
- iPhone 8 Plus, iOS: 12.2 - Reproduced
- iPhone XR, iOS: 12.0 - Reproduced

Reproduced on Unity 2018.2.0a1, 2018.2.21f1, 2018.3.14f1, 2018.4.5f1, 2019.1.11f1 and 2019.2.0b10