I was using Stingers before my first pair of ICONS. I think they are by far the best soft spike and FJ made a great decision going with them. I too would be interested in the reason why the course changed out your spikes.
It was Muirfield Village Stadium Course in Columbus Ohio, I asked the member I was with and he said that the course was concerned of people having the wrong softspikes and that sometimes you can bring diseases on the spikes so this way it remedies this situation...
Not certain if these makes sense but it is their course so they can do what they want!