country 20boy,

I'm guessing there's something gone wrong with the parallax, for whatever reason. Vertical stringing is often a sign of excess parallax, because the comb of the stock tends to keep our eye in vertical line with the reticle, but not so much up and down, unless we have a really firm cheek weld.

“Montana seems to me to be what a small boy would think Texas is like from hearing Texans.”
John Steinbeck