Infinite layout jitter when header snaps in place when scrolling slowly on "Files Changed" tab on pull request page

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Bug

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Reproduction

• On a mobile web browser (for me: Mobile Safari 18, on iOS 17)
• Open a pull request page, e.g. https://github.com/iterate-ch/cyberduck/pull/16498/files
• Select the "Files Changed" tab
• Scroll down until the header "x files changed" snaps into place (sticky position), and the code panel flows below it.

Actual

• ✅ If you scroll quite fast, it works fine → First scene in attached video
• ❌ If you scroll slowly, there is a certain pixel range (y-scroll-position) where a bug occurs → Later scenes in video
  • You experience layout trashing / jitter in an endless loop
  • It seems 2 or more CSS breakpoints and/or some JavaScript seem in conflict
  • The layout elements jump back and forth at high frequency (multiple times per second) as visible on the video attached

Infinite.layout.jitter.when.header.snaps.in.place.when.scrolling.slowly.on.Files.Changed.tab.on.Pull.Request.page.mp4

Workarround

• Scroll fast in the first place to not get into the bug.
• If you find yourself in the bug situation, you can get out of this by scrolling up again and then down again (not too slow to not trigger the bug again).

Expected

• You can scroll at any pace and head snapping in and out works without any layout jitter issues
• This big is minor, a it only happens when scrolling quite slow, but I nevertheless wanted to report it.
  • Note: It happened to me during real normal use. Not any intentional exaggerated testing.
  • For the video I reproduced it by scrolling extra slow with small increments.
  • But it happend in real life with normal scrolling speed, just reaching that "unlucky scroll position" naturally.

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