Hold up a second. Seems to me that your first two shots are right. I didn't see where you said you adjusted the scope after these two shots or more. I think I would suspect the rifle/bedding. What kind of ML is it? I am thinking that maybe the heated up barrel is causing a different pressure point or amount of pressure changing the harmonics which would change the POI. If you had the time and/or the patience I would shoot 2 shots only from a cold clean barrel. Make any necessary scope adjustment and wait about 15 - 30 mins and a thorough cleaning. Then shoot 2 more.