Reproduction steps:
1. Create a new project
2. Enable Use new Hierarchy window (Edit > Preferences… > General)
3. Right-click on Hierarchy top bar and enable Tag column
4. Enter Play mode and observe the Console

Actual result: “NullReferenceException: Object reference not set to an instance of an object” errors are thrown
Expected result: No errors or warnings are thrown

Reproducible with: 6000.4.0a3, 6000.5.0a2
Not reproducible with: 6000.3.0f1, 6000.4.0a2, 6000.4.0a5
Couldn’t reproduce with: 6000.0.63f1, 6000.2.14f1 (No Hierarchy V2)

Reproduced on: Windows 11, macOS Tahoe 26.1 (M4)

Note:

• Sometimes Play mode needs to be entered twice for the issue to reproduce on macOS