I went back the other day, and once again those same two spots (2A and 6A) were coned off. So was a third (3A). I tried them all, and all three worked. So I set the cones aside.
There was a Tesla employee charging a company model S, so I told him the situation and suggested that they check all three spots anyway, just in case the problem is intermittent and/or happens only for some cars and/or shows up only at high power. The connector in 3A did require two tries to seat correctly in my car's charging port.