You properly torqued them on install, which is great. But did you re-torque them again within 100 miles? Did you check them again after that? Because like any new wheel install, that’s required.
Spacers are no different than aluminum wheels. They’re supposed to be torqued at regular intervals.
I bought a new trailer earlier this year. Steel rims mind you. Before I left the lot I watched them torque all of the lug nuts to spec with a torque wrench, at their request. Then I had to sign a waiver saying I would check the torque again at 100 miles. No **** (I’m guessing some knucklehead tried to sue them). My drive home was more than 100 miles, but I wasn’t pulling off the freeway to torque lug nuts.
But you know what? When I checked them after I got home, a handful of lug nuts between the dual axles needed more torque. I literally watched the guy at the trailer dealer torque them to spec, heard the torque wrench click. They weren’t loose, but, they weren’t at spec anymore either. And that is why there are mileage intervals to check torque on new wheels. And that goes for new spacers too. If you don’t follow the torque check schedule, well, you haven’t installed and maintained them properly.
People blame the spacers, but I’d be willing to bet that the install/maintenance is the issue 99.9% of the time.