the pattern on the ring of the spacer looks a bit unusual.. like the wheel was rocking in and out to create that.. and finally it just gave way and bent the top
I'm thinking the wheel wasn't 100% flush on the spacer.. the bolts would still torque down "properly" (as you said) but there would be a small gap and the load of driving just worked the gap wider and wider until 4 of the bolts snapped and the wheel bent the lip of the spacer working itself off..
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