To reproduce:
1) Open attached project
2) Open the "MainMenu" scene
3) Select the "GOGame" GameObject
4) Click "Start Single Server" in the inspector
5) Click the Play button

It freezes

Reproduced in 2017.1.0f3, 2017.3.0f3, 2018.1.0b5

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Hello,

There are a number of issues in the Unity Editor when trying to interrupt/abort blocked threads. These issues have largely been addressed with the new scripting runtime (aka .NET/Mono Upgrade).

I have verified that this issue is indeed fixed when using the new scripting runtime. This issue will not be fixed in the legacy/old Mono scripting runtime.

Thanks,
Jonathan