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Debugging while Async method is running randomly causes the debugger to jump back to the initial breakpoint or crash




Priority: 2Necessary for shipping a final release


Severity: 1Crash, freeze, data loss, work stops

How to reproduce:
1. Open attached project "" and scene "AsyncRepro"
2. Open Visual Studio and attach the Unity Editor for debugging
3. In Visual Studio, place a breakpoint on line 75 (on int a = 1) and uncomment line 16
4. In Unity Editor, enter Play mode
5. In Visual Studio, press "Step Into" multiple times button (shortcut is F11)
6. Observe each Visual Studio line after each "Step Into"

Expected result: the debugger does not randomly reset after the "Step Into" or "Step Over" and does not crash at any point
Actual result: the debugger randomly resets after the "Step Into" or "Step Over" and occasionally crashes when jumping between Await/Async methods

Reproducible with: 2018.1.9f2, 2018.3.14f1, 2018.4.0f1, 2019.1.2f1, 2019.2.0b2, 2019.3.0a2
Could not test with: 2017.4.27f1, 2018.3.0a1, 2018.3.0b1 (Visual Studio does not find coresponding location, unable to debug)

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