I thought I was the only one! It is indeed laggy, and scrolling isn't as smooth as the rest of iOS. Also, most notably when you visit someone's profile, there's this weird lag/stutter when loading their tweets. It was like this before the update, but wasn't like this on a non 120fps iPad? You would think there would be no lag at all with the new iPads but now there is when there wasn't any in the first place? Weird.
The Facebook app is another culprit, not the scrolling, but when tapping to view comments on a post there's the same lag. It's as if the 120fps pronounces it more, but I don't recall seeing lag in these areas on devices without 120fps?