Development of strong ester (banana) flavor and aroma after 3.5 weeks in a keg

[zman_]

I brewed the northern brewer karma Citra session ipa kit a little over a month ago, kegged it just under a month ago and just recently (the past 5-7 days) it has drastically changed in aroma and flavor. It went from being floral citrus and hoppy to having an overwhelming aroma of sweet banana. The 1 gallon I brought to a party last weekend was good and had no hints of ester but pouring a pint tonight was a drastic difference. The crisp clean slightly sweet finish has been maintained throughout but the hop flavor has vanished or been masked entirely. The color and clarity of the beer is unchanged and the off flavor persisted through several pours.

Does anyone have experience with such a drastic change in flavor in such a short time while being in a keg?

Some info:

OG 1.052 (slightly high due to boiloff)
FG 1.012-1.010 (expected range)
S-05 yeast
Fermented around 65-67 for 2.5, 7d dry hop
Kegged 9/27 after cold crashing for 1.5 days
Keg force carbonated and kept between 41-43F ever since

This is my first brew so I am trying to understand what goes wrong so I can prevent it in the future but this has me stumped. All mentions of this off flavor say that it's characteristic of fermenting St too high a temperature which was 100% not the case and wouldn't explain it developing after all this time in a keg. Any help is greatly appreciated!