Things can certainly vary from flight to flight! Next time you are on it try the last two rows to see if there's more of a difference. I think being behind the last emergency exit has something to do with the colder temp. I found another trip report from several years back that mentions the same. But as others commented perhaps SQ is operating a higher overall cabin temp than in days past.

From the trip report: The only downside was that it got very cold. As it is right next to the door, it is freezing! But if you walk up two meters, just ahead of the door to row 95, it’s a perfect temperature

Edit to add that Mainly Miles has a comment on Row 96 being very cold (It's also listed as one of the worst seats! Was ok for me but it may not suit others).