Websocket server not getting all messages from client

Question

Using a .net console app, I've created a websocket server. And a separate app for the client end.

I've used this webpage to create the server side code (https://developer.mozilla.org/en-US/docs/Web/API/WebSockets_API/Writing_WebSocket_server). So my main function looks like this:

    public static void Main()
    {
        string ip = "127.0.0.1";
        int port = 80;
        var server = new TcpListener(IPAddress.Parse(ip), port);

        server.Start();
        Console.WriteLine("Server has started on {0}:{1}, Waiting for a connection...", ip, port);

        TcpClient client = server.AcceptTcpClient();
        Console.WriteLine("A client connected.");

        NetworkStream stream = client.GetStream();

        // enter to an infinite cycle to be able to handle every change in stream
        while (true)
        {
            while (!stream.DataAvailable) ;
            while (client.Available < 3) ; // match against "get"

            byte[] bytes = new byte[client.Available];
            stream.Read(bytes, 0, client.Available);
            string s = Encoding.UTF8.GetString(bytes);

            if (Regex.IsMatch(s, "^GET", RegexOptions.IgnoreCase))
            {
                Console.WriteLine("=====Handshaking from client=====\n{0}", s);

                // 1. Obtain the value of the "Sec-WebSocket-Key" request header without any leading or trailing whitespace
                // 2. Concatenate it with "258EAFA5-E914-47DA-95CA-C5AB0DC85B11" (a special GUID specified by RFC 6455)
                // 3. Compute SHA-1 and Base64 hash of the new value
                // 4. Write the hash back as the value of "Sec-WebSocket-Accept" response header in an HTTP response
                string swk = Regex.Match(s, "Sec-WebSocket-Key: (.*)").Groups[1].Value.Trim();
                string swka = swk + "258EAFA5-E914-47DA-95CA-C5AB0DC85B11";
                byte[] swkaSha1 = System.Security.Cryptography.SHA1.Create()
                    .ComputeHash(Encoding.UTF8.GetBytes(swka));
                string swkaSha1Base64 = Convert.ToBase64String(swkaSha1);

                // HTTP/1.1 defines the sequence CR LF as the end-of-line marker
                byte[] response = Encoding.UTF8.GetBytes(
                    "HTTP/1.1 101 Switching Protocols\r\n" +
                    "Connection: Upgrade\r\n" +
                    "Upgrade: websocket\r\n" +
                    "Sec-WebSocket-Accept: " + swkaSha1Base64 + "\r\n\r\n");

                stream.Write(response, 0, response.Length);
            }
            else
            {
                bool fin = (bytes[0] & 0b10000000) != 0,
                    mask = (bytes[1] & 0b10000000) !=
                           0; // must be true, "All messages from the client to the server have this bit set"

                int opcode = bytes[0] & 0b00001111, // expecting 1 - text message
                    msglen = bytes[1] - 128, // & 0111 1111
                    offset = 2;

                if (msglen == 126)
                {
                    // was ToUInt16(bytes, offset) but the result is incorrect
                    msglen = BitConverter.ToUInt16(new byte[] {bytes[3], bytes[2]}, 0);
                    offset = 4;
                }
                else if (msglen == 127)
                {
                    Console.WriteLine("TODO: msglen == 127, needs qword to store msglen");
                    // i don't really know the byte order, please edit this
                    // msglen = BitConverter.ToUInt64(new byte[] { bytes[5], bytes[4], bytes[3], bytes[2], bytes[9], bytes[8], bytes[7], bytes[6] }, 0);
                    // offset = 10;
                }

                if (msglen == 0)
                    Console.WriteLine("msglen == 0");
                else if (mask)
                {
                    byte[] decoded = new byte[msglen];
                    byte[] masks = new byte[4]
                        {bytes[offset], bytes[offset + 1], bytes[offset + 2], bytes[offset + 3]};
                    offset += 4;

                    for (int i = 0; i < msglen; ++i)
                        decoded[i] = (byte) (bytes[offset + i] ^ masks[i % 4]);

                    string text = Encoding.UTF8.GetString(decoded);
                    Console.WriteLine("{0}", text);
                }
                else
                    Console.WriteLine("mask bit not set");

                Console.WriteLine();
            }
        }
    }

My client side console app uses the Websocket-Sharp library (https://github.com/sta/websocket-sharp/). The main logic for it is:

        using (var ws = new WebSocketSharp.WebSocket("ws://localhost"))
        {
            ws.OnMessage += (sender, e) => Console.WriteLine("Server says: " + e.Data);

            ws.Connect();

            for (var i = 0; i < 1000; i++)
            {
                ws.Send($"hello {i}");
                Console.WriteLine($"hello {i}");
                //Thread.Sleep(2000);
            }
        }

The client successfully sends each of the 1000 messages but on the server side, it does not receive all the messages. There are huge gaps in the messages (i.e. they are not out of order, messages are missing).

Does anyone know why this would happen? Why are messages disappearing?