Maybe! But I've stared at that and I think I can see what went on.
First of all:
Two of the bolt securing locations look chowdered at the edge of the threads.
One of the four bolt hole locations looks chowdered inside the threads, then broke away in the same direction the chain is trying to rotate the wheel.
Looking at the one hole where we can see inside, it looks to be straight metal, nothing more.
So my conclusion is this:
- Bolts hollding sprocket were never chemically bonded (loctite)
- Bolts holding sprocket were allowed to come loose with time.
- Once bolts were loose, they allowed some radial movement and a small amount of axial play, which began to destroy the threads inside the holes.
- At some point later, the bolt holes had almost no threads, and only 1-2 bolts were partially secured. The user hit the bike with some power, and due to the imbalance of fastening faces, the chain torqued the sprocket which tore the remaining bolts out.
Proposed solution: loctite your bolts. I believe people blame whatever seems obvious or convenient at the time. Not because they have an agenda or anything, but bcause most people on the groups are quite new to failure analysis and other mechanical studies. In all likelihood, a grom hub treated the same way (loose bolts and unattended) would suffer the same fate.
What you CAN say is that tapping tolerances on a grom would be better leading to fewer loose bolt issues.
Oh, and you can see evidence of the sprocket wobble on the uneven tooth wear pattern. The outer edge of each groove is hammered really hard.