Reproduction steps:

1. Open the attached "Archive" project.
2. Make sure Target SDK in iOS Player Settings is set to Simulator SDK.
3. Build it to Xcode.
4. Run with Simulator.
- Application crashes when trying to access "UnityEngine.iOS.Device.advertisingIdentifier" property with Debug.Log:

* thread #1: tid = 0xdc57de, 0x000000010ed46f52 libsystem_c.dylib`strlen + 18, queue = 'com.apple.main-thread', stop reason = EXC_BAD_ACCESS (code=1, address=0x0)
frame #0: 0x000000010ed46f52 libsystem_c.dylib`strlen + 18
* frame #1: 0x0000000107d8974e ProductName`il2cpp::vm::String::NewWrapper(char const*) [inlined] il2cpp::vm::String::New(str=0x0000000000000000) + 5 at String.cpp:74 [opt]
frame #2: 0x0000000107d89749 ProductName`il2cpp::vm::String::NewWrapper(str=0x0000000000000000) + 9 at String.cpp:79 [opt]
frame #3: 0x0000000107645b9c ProductName`::Device_get_advertisingIdentifier_m593615903(__this=<unavailable>, method=<unavailable>) + 11 at Bulk_UnityEngine_0.cpp:6849 [opt]
...

Reproduced with:
- 5.2.5f1,
- 5.6.0b3;
- Simulator

Not reproducible with:
- iOS device

Notes:
- Full log attached in the edit.
- Couldn't test it with Mono2x, because it doesn't build with:
Cross compilation job UnityEngine.Networking.dll failed.
UnityEngine.UnityException: Failed AOT cross compiler