I have not played the Xbone version, but I am guessing the OP's problem is that the disengage button doesn't drop you out above a certain speed. If you are going too fast, you cannot safely disengage supercruise, and as such pressing the button displays a warning instead of dropping you out. You can override this by double tapping the disengage button, but you will take some hull damage when you drop out, and it will drop you exactly at your current position, rather than anything in range and locked onto. To drop out normally, you need to be going less than 1Mm/sec, and then disengage.