When the scrollbox as the child of multiple retainerboxes, the scroll isn't smoothing.
It can see issue with PIE only. If it run with standalone (or package build) is fine.
In SScrollBar::ExecuteOnUserScrolled, "TrackGeometry.AbsoluteToLocal(MouseEvent.GetScreenSpacePosition())[AxisId]" value seems to have a big difference between standalone and PIE.
1. Make a new widget BP and add retainerbox.
2. Add a retainerbox to the children of the retainerbox created in step1.
3. Add a scrollbox to the children of the retainerbox created in step2.
4. Add multiple text to the children of the scrollbox created in step3.
5. Set "Self Hit Test Invisible" to retainerboxes.
6. Open the level blueprint and add "create widget" and "add to viewport".
7. Set the widget in create widget.
8. When run with PIE, scrollbox doesn't scroll correctly (not smoothing).
It can see the attached repro project when you run with PIE.
There's no existing public thread on this issue, so head over toAnswerHub just mention UE-78882 in the post.