Why can a pannier bounce into your spokes? Don't the rack legs and rigid pannier back make that physically impossible as long as any part of the back is still attached to the top rails? How little clearance have you got between wheel and pannier? Or are Ortleibs not rigid-backed?
But if the main hooks have bounced off the rail and you've only got a krab holding a grab handle to some part of the rack you've got plenty of scope on a bouncy enough ride to unseat the panniers for them to twist in all sorts of unexpected directions. They won't be well constrained, and that's just a bit crap when locking hooks that avoid the basic possibility are easy to come by.
Orts are stiff backed.
And at £80 a pair this is really in "must do better" price territory. Carraduras are £20 cheaper a pair, Carradrys are a fiver more but a fair bit bigger, both lock on.
Often seen riding a bike around Dundee...