macOS 26.6, 26.7, 27.0 and 27.2 beta 1/2. Reproduced with Apple's SimpleURLFilter sample ("Filtering traffic by URL", WWDC25 session 234), built and run as a macOS app.
The sample never sets localizedDescription, so I added one line to ConfigurationModel.save(configuration:) before saveToPreferences():
sharedFilterManager.localizedDescription = "Sentinel Filter Name"
The property holds the value in memory: after loadFromPreferences(), the logged LocalizedStringResource still has key: "Sentinel Filter Name". But the effective configuration the system starts the session with has no localizedDescription — the session is named after the app:
name = SimpleURLFilter
applicationName = SimpleURLFilter
application = com.example.apple-samplecode.SimpleURLFilterTC3Q7MAJXF
(the rest of the nesessionmanager dump is the urlFilter dictionary, and it has no localizedDescription key).
System Settings > Network > Filters shows the filter as URLFilter, not "Sentinel Filter Name". The stored configuration (/Library/Preferences/com.apple.networkextension.plist) has no localizedDescription key either, and injecting one by hand does not survive a nesessionmanager restart.
Re-saving, removing and re-creating the configuration, and rebooting the Mac do not change the displayed name.
Expected: the docs describe localizedDescription as "A string containing a description of the URL filter", and WWDC25 session 234's code sample ("Configure and manage URL Filter") sets it this way (manager.localizedDescription = "Alice's URL Filter").
For comparison, a NETransparentProxyManager configuration on the same Mac persists localizedDescription as the configuration's Name in the same plist, while the URL filter configuration has no such field.
Filed as FB24987420.