OM,
If you were shooting good groups at your comfort level distance and feeling good about your shot executions, and nothing changed on your set up, i.e., your nock point didn't slide up, and your brace ht didn't changed (sometimes signaling a bowstring starting to go) then it has to be a change in your form.
I'm just going to guess that if you were experiencing exceptional success and enjoying your shooting, that you may have shot longer than normally, and/or, shot more arrows, either of which could have caused your ring finger to become sore. So, the next time you go out to shoot, you start to favor that sore finger which causes you to put different tension on the string with your other fingers.
Any change in tension on the string with any given finger can cause a difference in arrow flight; particularly common is the "nock high" flight you started experiencing.
I'd set your equipment back to where you started, and either give your finger some rest time, or, as I have done numerous times, tape up the 'offending' finger, and see if that relieves the discomfort.
A problem with continuing to shoot as you are, is that new, undesirable habits can develop that become hard to break once you're back to normal.
Good Luck, and Have Fun!