Could you elaborate on what you changed? We've changed the Data Protection Entitlement to NSFileProtectionCompleteUntilFirstUserAuthentication which solved the issue for us. Also, are you able to reproduce consistently? Yes, it's easily reproducible. Reproduction steps in our case: Launch the app and log in. Force quit the app. Wait. Somewhere in the next hour or so the prewarming will start, which in resolution will call application(_:didFinishLaunchingWithOptions:). As mentioned previously, in our case, we check for some UserDefaults flags there. If they do not exist then we do a complete cleanup (UserDefaults + Keychain). This caused users on iOS 15 to get logged out.

In the end, the issue turned out not to be related to Private Relay at all. It was caused by a combination of iOS 15 changes to app startup and app entitlements. See this answer for more info.

This answer solved this issue for us.

This answer solved this issue for us.