The CH-47 can provide a very good example of this problem as a pilot induced problem.
While shutting down, with the RRPM getting slow enough that, with a little head wind, the blades of the forward rotor head that have been held up by the wind till about the 1 O’clock position, come down on the droop stops with some force.
The pilot, ever wanting to minimize the pounding of the droop stops, tries to "fly" the rotor blades off the stops by adding aft cyclic, which works very well, for a little while.
Then all at once, the blade is moving slowly enough the head wind no longer holds the blade up. The blade comes down with force and can flex low enough across the top of the aircraft to hit the tunnel cover over the drive shaft.
And another hard day of explanations has begun.