[The HACK]

Also, to add to my previous point. It is entirely possible for the spacer to be the culprit in this case. If a spacer is machined to the wrong tolerances, for example, a chamfer edge few thousands of an inch too large to allow the wheel to sit completely flush with the face of the spacer, or imperfections on the spacer prevents the spacer from sitting completely flush with the hub face, or if the hub hole on the spacer is a few hundredth of an inch off allowing the spacer to sit unevenly on the hub nub when installed, any of the above spacer defect can easily lead to enough movement of either the wheel face or the spacer face to cause a complete bolt failure. And all it has to do is damage one single bolt to result in a similar catastrophic failure.

In cases like this, the most obvious damage is to the bolt itself. What leads to a single bolt failing (or multiple bolt failing) is up to speculation here. Whether it's inferior bolt, improper torque of the bolt, or spacer failure is impossible to determine at this point.