from the photo of the crash site it looked like there might have been in-flight breakup - I assume due to the sudden air loads beyond design limits.
As I mentioned earlier, large yaw oscillations could laterally flap the rotor (particularly on the 609) beyond its design limits of around 10 degrees and cause a wing strike which is why we see markers for "LH HIT" and "RH HIT" in the map, I presume.
this happened during "classic" flight mode, not transition. My uneducated guess would have been that this part of the flight envelope to be well understood and modeled.
Transition is arguably not the real tricky area as it happens at lower speeds - its high speed high dynamic load flight with flapping rotors where you typically get to the fringes.
That said, it is all highly dependent on specific rotor tuning where it would be most sensitive.