Hierarchy v2: Expand/Collapse doesn't work reliably.

In the Hierarchy window (HierarchyView), clicking a node's expand/collapse foldout toggle only works the first time. Clicking the same toggle again does nothing — the toggle glyph visually flips, but the node does not actually expand or collapse. Interacting with a different node "unsticks" it for exactly one more toggle.

Environment / important repro condition

  The bug only reproduces when nothing in the Editor is continuously updating ("dirtying") the scene. It is masked by anything that keeps the edit-mode player loop ticking (animated materials, active particle systems, [ExecuteAlways] scripts, realtime GI, etc.), which is why it does not reproduce in many projects.

• Windows: reproduces even with the Scene/Game views open.
• macOS: reproduces only when both the Scene view and Game view are closed (an open, rendering view keeps the loop
    ticking on macOS).

Steps to reproduce:

1. Open the Hierarchy test project: Tests/EditModeAndPlayModeTests/Hierarchy.
2. Open the scene Assets/Scenes/PrefabStyleTests.unity.
3. Make sure Hierarchy V2 is enabled if it is not the default.
4. Ensure nothing is continuously updating the scene. On macOS, close the Scene view and Game view. (On Windows this is not required.)
5. In the Hierarchy window, click the expand/collapse toggle of a node that has children → it expands (works).
6. Click the same toggle again → nothing happens (the arrow flips, but the node does not collapse).
7. Click the toggle of a different node, then return to the first node's toggle → it works once again, then sticks again.

Sometimes you have to click more than just a second time in step 6 to reproduce the issue, as if there is a background scene update it will not reproduce.

Actual results: Only the first click per node is honored; further clicks on the same node's toggle are ignored until a different node is interacted with.

Expected results: Every click on a foldout toggle expands or collapses that node.

Reproducible with versions: 6000.7.0a3, 6000.6.0b1, 6000.6.0a7

Not reproducible with versions: 6000.6.0a6

Can’t test with versions: 

Tested on (OS): Windows 11, MacOs

Notes:

Root cause

HierarchyView.OnExpandedStateChanged de-duplicates foldout clicks using a guard keyed on (Time.frameCount, node), intended to reject presumed click-spam / a spurious duplicate ClickEvent. In edit mode, Time.frameCount only advances when the edit-mode player loop runs (InternalUpdateScene, gated by IsUpdateNeeded()), which does not happen from Hierarchy input alone. In a "quiet" scene the frame counter is frozen between clicks, so the guard treats every second click on the same node as a duplicate and drops it. Additionally, no real duplicate ClickEvent actually occurs, so the guard provides no benefit.