Dan,
IF you question your form then you are most likely correct!!!! Conventional wisdom here on the internet is that spine is soooooo important. IT ISN'T!!! With good form ( read that as consistent form) you can shoot accurately several spine groups up or down and still hit what you are shooting at. Spine ONLY becomes important AFTER form -- NEVER before.
From your description, you have changed something in how you shoot. To be sure, a string change or arrow change MIGHT affect your shot but then it is is fairly common that you start to try to adjust that by changing (consciously or unconsciously) your form. It may be an unconscious change but change none the less.
Video can show what you may be doing. Look at it critically and see if what you think you are doing is what you are really doing.
IMO marginally spined arrows are not your problem.
Arne