I think a lot of these are the iOS26 bugs. On the iOS 26.1 public beta, things are significantly smoother. No flickering header, no non-responsive buttons, no sudden jumpy scrolling, etc.
Hopefully apple will release that update soon 
For context: the bug causes the entire geometry of the page to be wrong from the javascript/css point of view. Things which are “at the bottom” are not actually at the bottom visually. When you tap something, the click event goes to the wrong element. And those problems have a knock-on effect to all sorts of things, including our infinite scrolling system for posts in a topic.