"Failed to bind UDP socket" and "Host is shutting down" errors occure and UI locks when pressing "Start Host" on multiple Editor Multiplayer instances

Steps to reproduce:

1. Create a new project using Universal 3D template
2. Go to Window > Multiplayer > Multiplayer Center
3. Set the "Genre of your Game" to "Adventure" and Players to "2" (or any other options)
4. Click "Install Packages"
5. In the Quickstart tab, click "Create and open scene with netcode setup"
6. Open the Multiplayer Play Mode window (Window > Multiplayer > Multiplayer Play Mode) and enable "Player 2"
7. Enter Play mode in "NGO_Setup" scene
8. Press "Start Host" on both Editor instances
9. Observe the Console

Actual results: "Failed to bind UDP socket because the address is already in use.", "Server failed to bind" and "[Netcode] Host is shutting down due to network transport start failure of UnityTransport!" errors and cannot select "Start Client" instead, Play mode has to be exited and re-entered

Expected results: The port-in-use exception is caught more gracefully and a clear, user-friendly warning is logged, the UI state resets cleanly so the user can simply click "Start Client" without needing to restart Play Mode entirely

Reproducible with versions: 2.9.0, 2.11.0 (6000.0.71f1, 6000.3.12f1, 6000.4.1f1, 6000.5.0b1, 6000.6.0a1)

Tested on (OS): macOS 26.3

Notes:

• On few occasions, exiting and re-entering Play mode did not reset the state and threw errors afterwards