Posting my experience on the off chance it helps someone. One of the first things most of us probably learned when beginning archery was to square our feet. Somewhere down the line my stance got lost in the haze of working on more complicated form issues like elbow alignment and back tension. I first started noticing something was wrong when for the first time the string started hitting my nose. I looked to my anchor, which has always been consistent, then to the glaringly obvious: tilt, don't turn. At first I thought it the product of my straightening out considerably due to better elbow and back alignment, but of course *improving* form shouldn't lead to a problem. I finally had an epiphany when I realized just how much I was straining to look head on at the target when in my stance.
The best I can diagnose it is somewhere along the way I became too rigid in the whole "keep chest straight, only turn head" rule. For a lot of us squaring up is the *first* step of our shot, and, ironically, it remained mine also, but the fact that my body had gotten so used to doing it the wrong way made it automatic. It only takes a very small angling of the back foot and slightly too little rotation of the waste to really screw things up. Now that I opened my stance back up to a neutral/non-strained position every aspect of my shot has improved. No string on the nose, elbow alignment feels drastically easier, etc.
Just a cautionary tale in case anyone has some of the same symptoms as I did. Don't forget the basics!