jiska 🦄
Apple added a feature called "inactivity reboot" in iOS 18.1. This is implemented in keybagd and the AppleSEPKeyStore kernel extension. It seems to have nothing to do with phone/wireless network state. Keystore is used when unlocking the device. So if you don't unlock your iPhone for a while... it will reboot!
In the news: "Police Freak Out at iPhones Mysteriously Rebooting Themselves, Locking Cops Out"
https://www.404media.co/police-freak-out-at-iphones-mysteriously-rebooting-themselves-locking-cops-out/
iOS version diffs to see yourself:
https://github.com/search?q=repo%3Ablacktop%2Fipsw-diffs%20inactivity_reboot&type=code
Police Freak Out at iPhones Mysteriously Rebooting Themselves, Locking Cops Out
Law enforcement believe the activity, which makes it harder to then unlock the phones, may be due to a potential update in iOS 18 which tells nearby iPhones to reboot if they have not been in contact with a cellular network for some time, according to a document obtained by 404 Media.
ScreechingBagel