you said it was still stacked your 53gr , what is your twist rate? you need a fairly fast twist for 75gr like 1:7
a 1:9 could put you right on the edge of stability and the difference that puts you off could be very minor if you were already on the edge of stability.
My gun is a 1:7 twist which from my reading shouldn't shoot those 53's as well as it does but it does.
1:7 should stabilize a 75gr and be less than ideal for 53gr however those V-max tend to be a very concentric bullet that fly much faster form 22-250 than the 223 so spinning them faster twist but not higher speed probably doesn't effect them much.
I have found my 1:7 all shoot 55gr fairly well but I am not pushing velocity with anything.
I would chill some rounds down and see if that makes any difference easy test you already have rounds
the 8208xbr only has a 2.7gr range for start to max I would probably start over and load a 20.0, 20.5, 21 ,21.5 ,22 and look for a good group between 2 other good groups.
the other thing is and it costs money up front to shoot more bullets but it confirms the load , you can get lucky on a group especially of 3 but much harder to get lucky on groups of 5 harder yet on several groups of 5
I think if you shoot the test groups 10 at each of the 1/2 gr increments you will find a range where it is good , you can fine tune on that but in the middle of good has better practicality than the search for perfect.
few of us really need any better than MOA there was a long range competitor and instructor , who said you can search for sub MOA and it can be a perpetual quest but MOA will do. Better to have a load and rifle that is MOA all the time than one that is sub MOA when the stars align. spend your ammo learning your range and reading the wind than a quest for bench perfect condition sub MOA