Akin to resting your barrel on sandbags and trying to zero your gun and then hunting with it not rested on sandbags, attaching a big old heavy weight to the end of your barrel is apt to cause some POI shift. This may be from barrel droop because of the extra weight and/or from a change in the barrel harmonics caused by the attachment of the suppressor. Heavy bull barrels seem less affected than thin, pencil barrels, but this is not universal and with a longer barrel you are more apt to notice a change than with a shorter barrel. When a change does occur with the addition of a suppressor, the POI tend to be lower and from what I have seen usually left, thought I have seen some that end up low right as well. I seem to recall one guy on YouTube having a POI shift high right, but can't find the video now.