Fatal unhandled exception when using multiple subscriptions

[boexler]

Fatal unhandled exception thrown when using multiple subscriptions

   at System.Net.WebSockets.WebSocketBase.<SendAsyncCore>d__47.MoveNext()
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at GraphQL.Client.Http.Websocket.GraphQLHttpWebSocket.<SendWebSocketRequestAsync>d__32.MoveNext()
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at GraphQL.Client.Http.Websocket.GraphQLHttpWebSocket.<>c__DisplayClass29_1`1.<<CreateSubscriptionStream>b__7>d.MoveNext()
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
   at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
   at System.Threading.QueueUserWorkItemCallback.System.Threading.IThreadPoolWorkItem.ExecuteWorkItem()
   at System.Threading.ThreadPoolWorkQueue.Dispatch()

Following line seems to cause the issue (requests are not processed in serial):
https://github.com/graphql-dotnet/graphql-client/blob/master/src/GraphQL.Client/Websocket/GraphQLHttpWebSocket.cs#L87