Speaking from experience with flying model sailplanes, dynamic soaring, where we hold the world speed record for ALL model aircraft (504mph I believe) where we maintain huge circles on ridges in high winds, constantly flying through a boundary layer between the super high winds, and the lee side of the hill in knife edge orientation, which caused a LOT of "waggle" (what we called it), but we found that span loading (adding a bunch of weight to the wingtip leading edge area) solved two issues. First, it got rid of the waggle, and second, if helped with the aerodynamic forces wanting to twist the wing (leading edge up/washout).
Most other panes have wing tanks, which could also be considered a form of span loading.
The fact that our 12's have no wing tanks, and very light wings might contribute to turbulence having more of an affect than other planes with wing tanks, since all the main weight is at the center of the plane.
Here's a couple slow vids in the 300's (the fast vids you literally cannot see the plane it's going so fast) but you can see the plane waggle as it crosses the boundary layer.
Crank up the sound! Dynamic soaring is simply amazing!
https://www.youtube.com/watch?v=Vi0hrjqU15I
https://www.youtube.com/watch?v=WaQB16ZaNI4