Once you have the bottom nock and a little gap between your nock sets and arrow, start adjusting height and see what happens.
You can also go to paper tuning a fletched shaft a little just to see what is going on. Shots at 6’, 10’ and a little further can show if you have a big wobble in the arrow. Sometimes that can really show you some stuff that is happening before your eye can pick it up.
Make sure you are not plucking and dragging your ring finger particularly. That could really cause the nock end of the arrow flip out and down. At least I think that is what causes it when I get a bare shaft to do that like about an hour ago on one.
Also make sure you have a way weak arrow and make sure your start on the high side of nock height. Being way stiff on the arrow and low nock can really product a lot of odd stuff when I am tuning.