Steps to reproduce:

1. Open the attached project
2. Open the TestScene
3. In the Multiplayer Play Mode window, start a Virtual Player
4. Enter Play Mode
5. In the Virtual Player window, press the Layout button
6. Enable Hierarchy and the Inspector windows
7. Disable the Inspector window
8. Enable the Inspector window
9. Observe the Virtual Player window

Actual results: The hierarchy window is not displayed, and a warning about an issue is thrown

Expected results: The Hierarchy panel inside the Virtual Player window is displayed without warnings or errors after re-enabling the Inspector

Reproducible with versions: 2.0.0-pre.1 (6000.3.0b4, 6000.4.0a1)

Not reproducible with versions:  1.6.1 (6000.0.59f1, 6000.2.5f1)

Tested on (OS): macOS 26.0

Notes:

• The issue persists after exiting and re-entering Play mode. Clearing the Library folder temporarily resolves the issue
• Does not reproduce with Hierarchy V1. Hierarchy V2 can be enabled via Preferences -> General -> Use new Hierarchy Window

Full warning message:

• Attempted to open unsupported window in cloned player systems: Unity.Hierarchy.Editor.HierarchyWindow.Please reach out on the forums and contact Unity Admins for more info.

UnityEngine.Debug:LogWarning (object)
Unity.Multiplayer.PlayMode.Editor.ClonedPlayerSystems:BlockWindowIfRequired (UnityEditor.EditorWindow) (at /Users/bokken/build/output/unity/unity/Modules/MultiplayerEditor/Managed/MultiplayerPlayMode/Workflow/EditorSystems/ClonedPlayerSystems.cs:72)
Unity.Multiplayer.PlayMode.Editor.ClonedPlayerSystems:OnWindowChangedShouldBlock () (at /Users/bokken/build/output/unity/unity/Modules/MultiplayerEditor/Managed/MultiplayerPlayMode/Workflow/EditorSystems/ClonedPlayerSystems.cs:56)
UnityEditor.WindowLayout:TryLoadWindowLayout (string,UnityEditor.WindowLayout/LoadWindowLayoutFlags)
Unity.Multiplayer.PlayMode.Editor.WindowLayout:LoadWindowLayout (string,string) (at /Users/bokken/build/output/unity/unity/Modules/MultiplayerEditor/Managed/MultiplayerPlayMode/InternalBridge/WindowLayout.cs:35)
Unity.Multiplayer.PlayMode.Editor.EditorModesUtility:SwitchLayoutToMode (bool) (at /Users/bokken/build/output/unity/unity/Modules/MultiplayerEditor/Managed/MultiplayerPlayMode/Workflow/EditorModes/EditorModesUtility.cs:176)
Unity.Multiplayer.PlayMode.Editor.WindowLayoutPopoutWindow:OnUpdate () (at /Users/bokken/build/output/unity/unity/Modules/MultiplayerEditor/Managed/MultiplayerPlayMode/Workflow/UI/WindowLayoutPopoutWindow.cs:49)
Unity.Multiplayer.PlayMode.Editor.TopView/<>c__DisplayClass3_0:<CreateGUI>b__5 () (at /Users/bokken/build/output/unity/unity/Modules/MultiplayerEditor/Managed/MultiplayerPlayMode/Workflow/UI/TopView.cs:122)
UnityEditor.EditorApplication:Internal_CallUpdateFunctions () (at /Users/bokken/build/output/unity/unity/Editor/Mono/EditorApplication.cs:392)