Bear
As promised:
The mass of the released part is not nearly as important as its velocity and the shrapnel that accompanies it.
The idea was to fail-safe it to the point that it was extremely unlikely to fail.
Lots of considerations like; cyclic life, freedom from harmful vibrations, wear, fire and overspeed
Even then the aircraft is designed to minimize the impact to safe landing should the failure of this part occur. (good job there )
So what caused its release
keep track of the photos and press releases for any hints.
Lots is aleady available to the investigators from the recovered parts, although more part searching along the ground may be necessary.
No sense in speculating ahead of some more facts and "what ifs" are just that since the safety aspects are based on minimisation of combinations and not impractical flat out eliminination