How to reproduce:
1. Open attached "ThreadLostTest" project
2. Switch and build to iOS platform and run with an iOS device connected
3. Tap "Test 3000" button
4. Notice that logs message "DoSomethingAsync(): done result=True" is not being displayed on the screen

Expected result: DoSomethingAsync() was completed and show the message "DoSomethingAsync(): done result=True"
Actual result: DoSomethingAsync() freezes and the message "DoSomethingAsync(): done result=True" is not being shown on the screen

Reproducible with: 2018.4.3f1, 2019.1.8f1, 2019.2.0b8, 2019.3.0a8
* iPhone 8 Plus (iOS version 12.0)
* iPhone X (iOS version 12.1)

Not reproducible on Android Mono and IL2CPP scripting backend:
* Samsung Galaxy Note8 7.1.1
* Razer Phone 2 (Phone 2), Android 9, CPU: Snapdragon 845 SDM845, GPU: Adreno (TM) 630

Not reproducible in Editor Standalone