Problem with RichTextBox rendering

c#
public Main(TcpServer server)
{
    InitializeComponent();
    tcpServer = server;
    tcpServer.MessageReceived += TcpServer_MessageReceived;
}

private void TcpServer_MessageReceived(object sender, string message)
{
    Logger.Log("Received from client: " + message + "\n", TaskLogger);
}

c#
public Main(TcpServer server)
{
    InitializeComponent();
    tcpServer = server;
    tcpServer.MessageReceived += TcpServer_MessageReceived;
}

private void TcpServer_MessageReceived(object sender, string message)
{
    Logger.Log("Received from client: " + message + "\n", TaskLogger);
}

c#
public event EventHandler<string> MessageReceived;

c#
public event EventHandler<string> MessageReceived;

c#
private void HandleClientComm(object client)
{
    TcpClient tcpClient = (TcpClient)client;
    NetworkStream clientStream = tcpClient.GetStream();

    byte[] messageBuffer = new byte[4096];
    int bytesRead;

    while (true)
    {
        try
        {
            // read
            bytesRead = clientStream.Read(messageBuffer, 0, messageBuffer.Length);

            if (bytesRead == 0)
            {
                // disconnected
                break;
            }
            string receivedMessage = Encoding.ASCII.GetString(messageBuffer, 0, bytesRead);

            MessageReceived?.Invoke(this, receivedMessage);
        }
        catch (Exception ex)
        {
            // todo
            break;
        }
    }

    tcpClient.Close();
}

c#
private void HandleClientComm(object client)
{
    TcpClient tcpClient = (TcpClient)client;
    NetworkStream clientStream = tcpClient.GetStream();

    byte[] messageBuffer = new byte[4096];
    int bytesRead;

    while (true)
    {
        try
        {
            // read
            bytesRead = clientStream.Read(messageBuffer, 0, messageBuffer.Length);

            if (bytesRead == 0)
            {
                // disconnected
                break;
            }
            string receivedMessage = Encoding.ASCII.GetString(messageBuffer, 0, bytesRead);

            MessageReceived?.Invoke(this, receivedMessage);
        }
        catch (Exception ex)
        {
            // todo
            break;
        }
    }

    tcpClient.Close();
}