Multiplayer Play Mode Additional Editor instances crash when calling DisplayProgressBar() to display a Modal Window

How to reproduce:
1. Open the attached “CrashRepro“ project
2. Open the “Assets/Scenes/First.unity“ Scene
3. Open the “Multiplayer Play Mode” Window (Window > Multiplayer > Multiplayer Play Mode)
4. Enter Play Mode
5. Enable “Player 2“ in the MPM Window

Reproducible with: 1.6.1 (6000.2.6f1, 6000.2.9f1)
Not reproducible with: 1.6.1 (6000.0.62f1, 6000.2.5f1, 6000.2.12f1), 2.0.0 (6000.3.0f1, 6000.4.0a5, 6000.5.0a1)

Reproducible on: macOS Tahoe 26.0.1 (Intel), 15.6.1 (M4 Pro)(by user)
Not reproducible on: No other environment tested