*Steps to reproduce:*
# Create a new project
# Go to "File" ->"Build Profiles" 
# Resize the "Build Profiles" window (make it much bigger)
# Also, resize the "Platforms" section (make it wider)
# Dock the "Build Profiles" window next to the "Scene"
# Observe the "Build Profiles" window.

*Actual results:* Instead of one separation line, a user sees two. A few screenshots and a video are added below in the "Attachments" section.

*Expected results:* A user should always see one line.

*Reproducible with versions:* 6000.0.11f1, 6000.0.14f1.

*Not reproducible with versions:* 6000.0.10f1

*Can’t test with version:* 6000.0.8f1 because the line is stable in this version.

*Tested on (OS):* Sonoma 14.6

Culprit PR: https://github.cds.internal.unity3d.com/unity/unity/pull/46899
On this line:
 https://github.cds.internal.unity3d.com/unity/unity/blob/f08bf0a1a945c6ab8972030f7231b2ad4403e5bb/Modules/UIElements/Core/Controls/TwoPaneSplitView.cs#L466

The m_FixedPaneInitialDimension is not updated after the pane is resized, so the dragline is misaligned after resize. Reverting to the old code that uses dimension would fix this, but I am not aware of other caveats in this, so I am assigning this back to the original author.