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.
Parallax seems to be the consensus. I'm going to swap some scopes around later this week and try again. I'll keep you posted, but it looks like this one is headed back to Oregon for repairs......