Same with doing cliff winching in an updraft in the Sea King Syd - no chance of reading any instruments at all.
However
because the inflow angle only changes at the front of the rotor disc
the inflow angle changes at the rear as well with the front seeing a bigger change than the rear, hence the dissymmetry.
Normally the vibration is associated with translational lift rather than inflow roll.
In a still air transition the inflow roll happens first, then the flapback and then, when you overcome both, the vibration of ETL.