Admiral - I have always had a bottle of Longmorn on the go - and consider it one of my all-time favourites. I have not noticed that "explosive" "fire". My usual associations would be a warm peppery bright mouth feel with tangerine and orange rind - even roasted red pepper and honey, with a smooth long balanced finish. But hey, that's just my palate, and I know it has evolved over the last couple of years with increased exposure to a broader range of whisky. Your palate may have had some rare and unique experiences over that last couple of years that now are being impacted by this new bottle. I have no doubt you know your way around the whisky spectrum.
What I have noticed is how impressionable some of the more subtle malts - like wine - are to the state of our taste-buds and our noses - and how other things: food, other drinks, weather, a head-cold or flu, atmospheric conditions, even proximity to perfume or cologne and even how recently I brushed my teeth, for example, can be an influence. But that's me
. I wouldn't give up on it yet, but might suggest re-examining the circumstances of this experience and see if it repeats over several tastings, say several times a day - for several days.
(And take notes!!!)
Failing that - send your fiery bottle my way and I'll do my best to analyze it for you. I promise to return the empty!!!