One thing to add to EMRI's post, check for a bent tube. If there is a bend in the tube, or scratches or wear marks, the tube doesn't go back into the same place every shot. Then it will climb up at a 45 degree angle.

Second, if you are using a commerial benchrest that has a screw adjustments, make sure everything is locked down tight! Loose rest can cause this stringing, but I've never heard of one that goes up and right then up and left, usually just one directing.

HTH, Ric