But I think the frame drop occurred with the last update so it has to be related to that update, or am I wrong there?
Very likely, yes. That doesn't necessarily mean that it was the stuff that was added in the last update though.
We continually optimize code, make updates to cheat detection, have integrated new crash reporting pipelines, modify code to support new features, and make loads of other behind-the-scenes changes during an update, so while players tend to see the shiny new things and think that must be the source of the problem, that's not always the case. We gather data, find the sticking points, and address them that way.
This is a game with millions of lines of code and a lot of interconnected systems mean that sometimes things fall over, or sometimes we optimize an area that runs better in one place, but has knock-on effects in another.