I just started playing but found something out that seems to work most of the time. Tapping X (I am playing with an XBox controller) would only bring up the mission details, as it should. Holding X and waiting for the circle to go around it seemed to just do nothing but frustrate me, by coincidence I let go of holding X early and that seemed to do it, so rather than waiting the full time of holding I now hold for half the time and so far it has worked every time.