That looks to me like the effect you get when the browser does scrolling on a totally different thread (most do these days) and the pinning is done using transforms (which is the default when you're pinning inside a scroller that's not the root because often those have transforms applied which ruins position: fixed). The browser repaints from the other thread and then when it executes JavaScript on the main thread, you see it suddenly corrects things. Super annoying. As far as I know, it's compl
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