I have kind of a strange issue. So I brewed a hefeweizen recently which came out pretty well. I used Wyeast 3068 pitched from a 2l starter.
It came in pretty nice when all was said and done, a touch of banana and some other esters which were really only present in the aroma (slightly so in the flavor, but as I understand it, still in style).
It fermented until terminal gravity, aged for 1 week, and transferred to a keg. Carbed it up over 2 weeks, and kept the keg at about ~40. It had the ester profile for about ~2 weeks but the strangest thing happened. I drew a pint yesterday, and it had almost 0 ester aroma or flavor... it was gone.
The other thing I noticed is that the yeast dropped out of suspension completely (crystal clear). I was able to just invert the keg which solved that problem, but I didn't expect it to drop. The last time I this yeast it stayed in suspension almost the entire time I had it in the keg.