If the serving is thicker and or thinner than before it may be your release at anchor and adjusting your brain and fingers communication to new thickness,kinda like a pressure switch. make sure you hit your same anchor as with other serving, I have found it all starts with the fingers ,,Just had the same problem..And I do believe that the tightness or looseness on the nock my have a little to do with it.. but I would make certain of anchor point first, that is if nock height definitely is the same as before...weird how our brains program..