yep, happened to mine a while back
basically the captive nut within the chassis that the subframe bolts into shears its welds meaning you cant get any real purchase on the nut. i.e. u cant tighten it fully, it'll just keep turning
i took mine to a welder my mechanic recommended and he simply cut a whole in the chassis re-welded the captive nut then welded the cut hole in the chassis
cost me ?40 for one side