How bloody tight were they?

I have some of those very same dodgy spacers on the front wheels of my car. Sure they're cast aluminum from china, but I don't worry about them ever. Use of different lug nuts can have very signifignat consequences. My 280zx turbo wheels needed a 3/8" spacer, kinda thick, and I still relieved the wheel a little to clear the caliper. But what I discovered was the OEM lugnuts - special ones for OEM mag wheels my studs were too short to have enough threads to be safe, about 9 turns I think is the minimum you wanted, i got like 7? anyways... got some aftermarket mag wheel lugs and they were threaded all the way down, adding like 4 more turns getting me a bit more comfortably into the safe to use area.

I wonder if there was very little thread engaged and it pulled the thread out of the bolt or the lug. that could cause a simultaneous failure of several or all the nuts, and have everything look ok.

I could be wrong, but I get strange exotic failures of things so I'm used to finding out why things went bad.