Reproduction steps:
1. Open the "Server.zip" project in VS and start the server
2. Open the "bug.zip" project
3. Open the only scene
4. Play the scene
-Notice in the console that there are no errors, however, the script stops running.
5. Uncomment Try-Catch block and play the scene again
-Notice the Unity exception from the try-catch block in the console.

The message produced by the exception: UnityEngine.UnityException: EnsureRunningOnMainThread can only be called from the main thread

Actual result: No errors are thrown in the console.
Expected result: Exception is handles and error is thrown in the console

Note: In 5.3 the asynchronous methods produce no exceptions and keep running after exiting play mode

Reproduced on: 5.6.0a1, 5.5.0b10, 5.4.2p3.