I irratic flight from arrow pinch happens when the arrow leaves the string because the nock is not in it's full position. If you wonder if you have arrow pinch simple pull your bow with an arrow on to full draw as you normally would and anchor, now let up on the bow and do not release. Is your nock still in position, or did it start to slip off the string somewhat?

I am very prone to it because of the somewhat short A to A and long draw length on my compound. Not a big problem with my 66 inch longbow.