Reproduction steps:
1. Create a new project
2. Edit > Project Settings… > UI Toolkit
3. Enable Hierarchy Integration
4. Create UI Document GameObject in the Hierarchy
5. Click on UI Document child GameObject

Actual result: “[UI Toolkit] Could not set value for target of type 'VisualTreeAssetInspector' at path 'VisualTreeAsset'...” warnings are thrown
Expected result: No errors or warnings are thrown

Reproducible with: 6000.5.0a4
Not reproducible with: 6000.3.3f1, 6000.4.0b3, 6000.5.0a3
Couldn’t reproduce with: 6000.0.65f1 (No Hierarchy Integration)

Reproduced on: macOS Tahoe 26.2 (M4)
Notes:

• Full warnings when no UI Document Source Asset is attached:

{code:java}
[UI Toolkit] Could not set value for target of type 'VisualTreeAssetInspector' at path 'VisualTreeAsset': conversion failed. (InspectorWindow)
UnityEditor.GUIView:ProcessEvent (UnityEngine.EntityId,intptr,bool&) (at /Users/bokken/build/output/unity/unity/Editor/Mono/GUIView.cs:70) {code}
{code:java}
[UI Toolkit] Could not set value for target of type 'VisualTreeAssetInspector' at path 'VisualTreeAsset': conversion failed. (InspectorWindow)
UnityEditor.RetainedMode:UpdateSchedulers () (at /Users/bokken/build/output/unity/unity/Modules/UIElementsEditor/RetainedMode.cs:43) {code}

• Full warnings when UI Document Source Asset is attached:

{code:java}
[UI Toolkit] Could not set value for target of type 'VisualTreeAssetInspector' at path 'VisualTreeAsset': could not convert from type 'UIDocument' to type 'VisualTreeAsset'. (InspectorWindow)
UnityEditor.GUIView:ProcessEvent (UnityEngine.EntityId,intptr,bool&) (at /Users/bokken/build/output/unity/unity/Editor/Mono/GUIView.cs:70) {code}
{code:java}
[UI Toolkit] Could not set value for target of type 'VisualTreeAssetInspector' at path 'VisualTreeAsset': could not convert from type 'UIDocument' to type 'VisualTreeAsset'. (InspectorWindow)
UnityEditor.RetainedMode:UpdateSchedulers () (at /Users/bokken/build/output/unity/unity/Modules/UIElementsEditor/RetainedMode.cs:43) {code}

• Warnings are being spammed as long as child GameObject is selected