Not surprised in the least it's why companies spend so much in wind tunnels tall screens are notoriously finicky,over the years I've had the same problem on several bikes and do at the moment where I have gone from Arai Corsair to an RX7GP they look identical and yet their a world away from each other,nothing has changed in my situation except the helmet.

Take the spoilers off and go from there in the end it's down to priorities of what you want.

More just as an insight as to what is going on do you have a tankbag if you do and fit it,fill it full of newspaper I bet it cures the problem because it'll stop the wind swirling behind the screen.