The header of a frame cannot be read from the stream

This WebSocketException "The header of a frame cannot be read from the stream" is always thrown when closing the web socket client.

I have an example of a websocket client sending and receiving the same message from the backend.

WebSocketClient
using (var ws = new WebSocket ("wss://localhost:44398/ws"))
{
ws.OnMessage += (sender, e) =>
Console.WriteLine ("Received Message: " + e.Data);
ws.Connect ();
ws.Send ("Test Message");
Console.ReadKey();
}

Backend
It is an asp.net core web application which only receive the request from the WebSocketClient and it answers back with the same message.

It returns the message as expected, but then after entered any key to continue with the execution it fails and throws the above exception at the time of closing the web socket client.

Here is the the code if you would like to take a look.
https://github.com/juanrivera2306/WebSocketSample

There is a README.txt file with the instructions to run the example.

I really appreciate any help you can provide.

Start with the linked WebSocketSample repository and its README.txt, then reproduce the failure from WebSocketClient when the using block closes after Console.ReadKey(). Compare that close path with the backend's echoed-message behavior; done means the sample can close the client without the reported WebSocketException.