I have been using a Yost Tab. Today I did some shooting with a Jenkins that I used to shoot. Was surprised to see that my impact was a good 3" left and a few inches high at 20 yards. Went back and forth between the two tabs to make sure it wasn't just me. Surprised since they are very similar design.
I doubt if it was any difference between the tabs, per se. You're probably changing something in your form, with knowing it. For example, if I torque the string, my impact is 3" left. When I hit 3" left, the first thing I check is if I was torquing the string, by shooting another shot while making sure I'm not torquing the string, because it's not something I'm aware of unless I'm checking it.
I use the Jenkins tab, and you might have a completely different reason for impacting 3" left. But changing anything can make your mind play tricks on you.