It is definitely accuracy issue. With out suppressor 3 shot groups are 1/2 or so at 50 yards, With suppressor 12 - 15 inch groups. I talked to shop where I got it they said need a h3 buffer. I switched it out and no difference
Either an alignment problem of the suppressor on the barrel, or inside the suppressor. Most likely a baffle strike. Holes in the target are most likely not round.
300 Blackout, not just for sub-sonics.
As stated above, this has to be an alignment issue. The buffer is not going to cause this level of change in POI, nor will the gas pressure. Both of these could affect POI but in a precision rifle where your measuring1/16 of an inch. Have you checked the target to see if you are getting a round hole,or oblong. Did you by any chance weigh the can before shooting it? If so you could check weight to see how much it has increased. Also did you check the can while you were firing? I have had some QD cans loosen after 2-3 shots and direct attach after as few as 5 shots. I have had a Liberty Torch loosen on an M-16, now can has 2 holes in the end!! I shoot 300 BO and 308 subs and never had POI change more than 1/2-3/4" with can versus no can, with either bolt or semi auto rifles. I would try it on some other barrel, since it is either loose, or the barrel threading is off- As a side note I would not suggest putting it on a AK pattern rifle, before you check the threads. Be SAfe,