So much of this challenge we have chosen is mental. At some point in most shooter's travel down the traditional path, focus and concentration play a much larger role than the form that has become little more than muscle memory. I know there are days when I can't miss...and days when my mind wanders while trying to focus and I'm lucky to hit water from a boat. For me, it's certainly a focus issue.
I find that varying practice helps improve confidence as well as shooting. I'll try a few shots at a large round bale, trying to pick spots on the bale that are difficult to focus on. This has helped my "spot picking" ability on game...something I find very difficult to do. I also shoot at tiny targets,(the little v8 cans are my favorite)to prove to myself that I can hit something small and my "shooting" (form etc.) is not the culprit when shots go awry. It's difficult enough to focus on a tiny target and hit it...but I find it's really difficult to pick a tiny, imaginary spot on a larg blank target and hit it.
So, do you think yours a mental issue...or possibly the "aim small, miss small" concept? You may be picking a much smaller spot to concentrate on with the animal targets and the opposite for the bullseye.