Perhaps the rebound is explained by the angle from the hoist - if the aircraft climbs to deploy the hi-line then the angle is steep and the hook has a long way to go vertically to reach the rotor.
If, on the other hand, the aircraft is moved laterally as the hi-line is deployed, the vertical distance is much lower - ISTR the report mentions the winch wire being snatched from the winchop's hand - that would correlate with the hi-line snagging and then parting.
Or it could well be a problem with the hi-line itself or a combination of the two issues.
I’m happy to see we can agree on some things Crab.
The hi-line snagged and as it came taut the hook was moving upward. The weak link parted with almost no load which allowed the hook to continue its upward trajectory. Momentum is a powerful force.