[It] turns out [that] Blitzwing has a factory assembly error - his biceps are switched. Just pop his arms off below the bicep swivel, pop the arms back on to the opposite sockets, and then switch his forearms (one screw, no glue).

If the biceps are correct, you will see the ball joint "vent" on the outside as show here:




[The] robot mode gets a little more clearance between the arms and the folded down wings after the swap.

[The] jet mode lines up much nicer. Of note, the flaps near the tail now line up vertically with top of the plane, and the front of the jet now sits flush on top of the wings:








And as you can see, the look of 'bot mode is not hurt: