Hi Longboarder. Did you bring the fault to the sommelier's attention? Here's what I would have said, after a lot of second-guessing myself, "I'm getting a lot of SO2 in this wine and, unfortunately, it doesn't seem to have blown off with decanting. Have you had this problem before? What do you think?"
And it could be that you have an exceptionally low identification threshold for SO2. The sommelier might have a higher threshold and may not sense it. Restaurants that value good customer should give you a new bottle of the same wine.