Well, I have the HDCP error when I try to connect the phone to a Miracast donge, while my other phones (Lenovo, Generic Chinese, Motorola) Can connect without problem. HDCP requirement should be optional and not mandatory. I expect that a high end phone could perform and behave equally than lower end phones.
In other issue, after tried to connect to Miracast, the screen wont turn off after you press the button, no matter how much time you wait (I set it to 1 minute). ¿Fix?, reboot.
Please include this two fixed in new revision of Marshmallow.