Squawk7000 - I guess this is the paragraph you are referring to in that report
Although the precise forces and moments involved in failing the helicopter structure have not been quantified, calculation has shown that, if the engine affected is neither automatically nor (rapidly) manually shutdown, rapid re-engagement of a slipping freewheel has the potential to cause structural failure of the tail boom. Defining such forces is difficult because the exact timeframe over which the re-engagement occurs has a significant effect on the torque felt through the transmission and by the airframe; an instantaneous re‑engagement would theoretically generate an infinite load. Physical examination of the components could not refine the time parameter, but calculations suggested that a re-engagement occurring over a fraction of a second could cause structural airframe damage.
So a slipping freewheel suddenly biting again could generate the forces required to make the tail boom fail.
Re-introducing two components turning at different speeds when they are designed to drive at the same speeds is a recipe for disaster - see the Wessex crash in the Welsh lake back in the early 90s - that was a disconnect coupling allowing the TR to slow down and then taking up the drive again as the yaw input was changed.