If your groups are tight, I would go with the others and think that your new 3 under anchor is causing the nock of the arrow to be to the right of where it was when you shot split (assuming you are a RH shooter). You can either work on getting the arrow back under your eye, or tilt your head over the arrow if that's not possible.
If your groups are not tight, you may have picked up some form issues when you switched, just because of the different feel of the shot. There are a lot of form issues that could cause a RH shooter to impact left: torqueing the string or bow, not getting the string elbow back behind the arrow, creeping, peaking, alignment, etc. These things tend to sneak in from time to time, even when we don't change anything, but changing something makes us focus more on whatever it is that we changed and forget to focus on some other things that are important.