Unless of course the mod is comming loose after a few zeroing shots as it heats up,and I have seen it (admittedly) only once or twice where a rifle has shot like crap with a certain moderator on, only to shoot very well when it has been swapped for another make,it could of course be a scope problem,try another scope and see how it performs then.
Hi yes you have a point if it was one gun and mod but the o/p said it was two guns that were doing the same so it looks like the mod not the scope and if they were comeing loose they must have checked for that its the first thing you would look at.