Mine is a V-Mach stage 1 kit ... home fitted but again it comes all pre lubed and I just dropped it in.
Just to add that I've tried to replicate this to see if it is me. I've tried tensing up to see if that does it ... I've tried snatching the trigger. Holding the rifle really tight and all other sorts of weird stuff. All of these make my groups poor but there is no way I can replicate the groups being very good but moving a precise amount vertically and then moving a precise amount back again. So I'm convinced it's something on the rifle/stock.
On my FT style stock there is only one pin at the trigger end. A large bolt that goes through the stock and fixes in that lug. No rear trigger pin as there is no trigger guard ... it's built in the stock. I used to have this very same action in a self made custom thumbhole stock but that stock had a trigger guard and two trigger pins. I used the gun in that stock for about 2 Winters and I can't remember it ever losing it's zero. I just turned up week after week and the zero would be good. So maybe that is suggesting that it's something to do with this Ft stock ... However, since taking it out of that thumbhole stock the action has had this more recent V-Mach kit fitted. So that's telling me it's either this FT stock or the V-Mach kit? Or it could be some 3rd option.
I suppose it's logical to put it in that old thumbhole stock to see if that eliminates the problem as that will prove it's something to do with that FT stock.