You should have someone stand behind you when you take your stance on the target. They can place either a straight edge, or an unfletched arrow across your shoulder blades. That'll show where you are really pointing. Your natural movement of your bow arm will fall back to this natural line. If your shoulders and torso are pointing left you are having to muscle over to the center and at release your bow arm goes left. I take an open stance and rotate my upper body into proper alignment. It's part of my shot process . I can immediately tell when I'm out of alignment at the shot.
You aren't plucking the shot either are you? Best thing is to get your body alignment nailed down, and video your shot sequence. You can cover a wide range of spines with a consistent release and form. Point weight changes are easy. But, without seeing you shoot it's a guess from everyone here as to what the one thing, or combination of things, it could be.
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