[Webkit-unassigned] [Bug 246048] New: Incorrect scroll position reported

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=246048

            Bug ID: 246048
           Summary: Incorrect scroll position reported
           Product: WebKit
           Version: Safari 15
          Hardware: iPhone / iPad
                OS: iOS 15
            Status: NEW
          Severity: Major
          Priority: P2
         Component: Scrolling
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: jack at greensock.com
                CC: simon.fraser at apple.com

Simple test case: 
https://codepen.io/GreenSock/pen/VwxxwWm?editors=0010

Scroll on any iOS device relatively quickly up and down. Notice the blue bar bounces around like crazy rather than staying "stuck". The scroll position seems to be incorrectly reported or rendering is happening out-of-sync.

Challenge: can you please recommend a way to keep the blue bar "stuck" using transforms? I can't use something like position: fixed because the container may have a transform applied. sticky isn't an option either. I need a way to get the correct scroll position and apply it at the correct time to make that element appear frozen while scrolling its container. 

Help?! 

I've reached out directly to the Safari team at least 5 times over the past few months and never receive an answer, so I'm posting a bug report here. 

I have no idea if these are related to this issue, but here are several other reduced test cases showing various scroll-related bugs/inconsistencies in iOS Safari: 

- https://codepen.io/GreenSock/pen/XWajYwG/16c435b12ef09c38125204818e7b45fc
- https://codepen.io/GreenSock/pen/ExbrPNa/087cef197dc35445a0951e8935c41503
- https://codepen.io/GreenSock/pen/JjOxYpQ/3dd65ccec5a60f1d862c355d84d14562

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