Main thread stack from hang dump:

ntdll.dll!RtlEnterCriticalSection()
Unity.exe!PersistentManager::IsObjectAvailable(int heapID) Line 1977
Unity.exe!GameObject::CheckConsistency() Line 765
Unity.exe!PersistentManager::CheckConsistencyObjectAndUnlockIntegrationMutexInternal(int instanceID) Line 1252
Unity.exe!TimeSliceAwakeFromLoadQueue::IntegrateTimeSliced(int timeoutMS) Line 144
Unity.exe!LoadSceneOperation::IntegrateTimeSliced(int timeSliceMS) Line 264
Unity.exe!PreloadManager::UpdatePreloadingSingleStep(PreloadManager::UpdatePreloadingFlags flags, int timeSliceMs) Line 454
Unity.exe!PreloadManager::WaitForAllAsyncOperationsToComplete() Line 561
Unity.exe!EditorSceneManager::RestoreSceneBackups(std::vector<EditorSceneManager::SceneBackup,stl_allocator<EditorSceneManager::SceneBackup,105,16> > & sceneBackups, EditorSceneManager::PlayModeChange mode, bool scriptsCouldBeChanged) Line 1021
Unity.exe!PlayerLoopController::EnterPlayMode(bool scriptsWereRecompiled) Line 468
Unity.exe!PlayerLoopController::SetIsPlaying(bool isPlaying) Line 361
Unity.exe!Application::TickTimer() Line 1952
Unity.exe!MainMessageLoop() Line 414
Unity.exe!WinMain(HINSTANCE__ * hInst, HINSTANCE__ * hPrev, char * szCmdLine, int nCmdShow) Line 1018