I have seen the same thing and think I figured it out. I alway push my knob to the left and yesterday I thought I would push it to the right. Well all of a sudden the POI moved to the left. I thought it must be me so I reevaluated my shooting posture and made sure everything was correct. I was shooting from a camera tripod with a V support and seated in a hard stable chair. And sure enough were it had been shooting on hole dead on the cross hair it was now shooting one hole group but 1/4″ to the left.
My cocking knob sits up against the top hat firmly. The knob sits up against the frame firmly. So what I did was to take off the knob and thin down the spacer around the threaded portion and then I sand the bottom of the knob enough to where it did not contact the frame at all when pushed to the side. Now the knob will click and seat to the top hat and when pushed to the side there is no resistance at all where before it was a firm push to move it over.
I just check it this morning and it is back to shooting one hole groups no matter what postition the knob is placed. I hope that was the actually cause of the problem, but for now it is dead ball accurate making one hole groups with no shifting at all.
I have recently adjusted my top hat and I attribute the new top hat setting to causing the increase resistance betweent he knob and frame.
Hope this helps!