We run simple iOS Swift code triggered by a remote notification: UserDefaults.standard.set("key", forKey: "value") It runs fine when the app is active or inactive, but when the device is closed/locked and the code is triggered, we see a warning in Xcode: Couldn't write values for keys ( key ) in CFPrefsPlistSource<0x3018802d0> (Domain: com.example, User: kCFPreferencesCurrentUser, ByHost: No, Container: (null), Contents Need Refresh: No): Path not accessible Not updating lastKnownShmemState in CFPrefsPlistSource<0x3018802d0> (Domain: com.example, User: kCFPreferencesCurrentUser, ByHost: No, Container: (null), Contents Need Refresh: No): 767 -> 767 The issue is that there seems to be no way to catch that warning. The value is set, when it's re-read the value is correct. But the value is never written to disk, so after an app restart/update the value is gone, potentially has an old wrong value. This code runs without any interruption, it's just showing the warning on iOS 17.7.1 on iPad: UserDefaults.standard.set("key", forKey: "value") UserDefaults.standard.synchronize() print("value: \(UserDefaults.standard.string(forKey: "key"))") Should there not be a way to catch this, so the code can act accordingly to the circumstances? It would be good to know inside the code that the value is not persisted. I would expect that an exception is generated somewhere which can be caught. It seems .completeFileProtectionUntilFirstUserAuthentication enables files to be written to disk while the device is closed/locked, can something similar be used for UserDefaults.standard?