Hi,
I got the bug when after timeout the client connection was not closed, it hangs for long time inside ReadAsync. Even when cancellation token was raised. I see your notice in the MqttTcpChannel.Dispose() method about stream disposing, but it should be like:

_stream?.Dispose();
_stream = null;

_socket?.Dispose();
_socket = null;

Disposing only _stream does not cancel ReadAsync in my case, so _socket should be also disposed.