From the look of the plant, I am guessing that it was just normal. The leaf probably had some fertilizer burn, when you got it and the vendor cut the end of the leaf tip off to make the plant look good to sell. Of course there will be other opinions too, but if you have sprayed and isolated the plant, you have done what you need to do. If it continues to show signs of stress, it is time to repot and see what is going on with the roots. JMHO.