I guess I'll throw in my 2 cents too.

The weight of the scope may be retarding the lift and seperation of the barrels causing it to cross. Take off the scope and see how that works.

To low of pressure can cause the barrels to flip at a slower rate thus allowing the bullets to cross.

To high pressure doesn't allow the bullet to stay in the barrel as long and the bullets can cross.

Pressure that is just right can allow the bullets to cross just because they want to.