I did wonder what kind of load that was being placed on the rotors!
I think it will be the airframe that is taking the strain rather than the rotors, which just provide the thrust.
The HUMS will have monitored the engines and gearboxes carefully and probably the total G experienced by the fuselage but with two rotors twisting, shaking and pulling the fuselage in different directions, especially in some of those very punchy manoeuvres - it's not a surprise that cracks appear - display flying might not have been included in the planned usage and operational profiles designed to predict fatigue issues.
Great display though.