Could be that off-note you experienced was due to a defective bottle. The defect could be too much air during filling, presence of bacteria in the wash, who knows what else. I've experienced this myself from time-to-time, tastes to me almost like new plastic water bottle, perhaps peroxide. Not pleasant, overwhelms the tastebuds.

One of my bottles in my collection had this defect. I contacted the distillery, who replaced my bottle with a fresh one via their distributor. Could be worth the effort to replace your bottle from Laphroaig, if you suspect it could be a defect.