I consistently hit this failed assertion in the lsw aggregation test because the test never reaches the final IndividualAggregator:individuals-changed signal handler for the linking:

      timer_id = Timeout.add_seconds (5, () =>
        {
          assert_not_reached ();
        });
      main_loop.run ();
      Source.remove (timer_id);

      this._lsw_backend.tear_down ();

(ie, the final timeout check)

It's not clear why the individuals-changed signal doesn't fire the second time.