https://wccftech.com/google-android-8-1-factory-reset/

Android 8.1 Developer Preview brought a slew of new features and changes, but it has not been free from bugs. Yesterday, a Reddit users reported an odd incident which led many users to believe that Android 8.1 Developer Preview has changed the default behaviour of Factory Reset Protection, which is Android’s anti-theft function. While other users think that this is just some bug acting up in the preview and Google shall fix it in the next update.

It’s worth noting that the Factory Reset Protection has worked as an anti-theft feature since the Android version 5.1 Lollipop. It makes sure that the user’s Google account is left untouched even after factory reset so that the password of the Google account has to be entered for setting up and using the phone. If the user does not know the password, then there is nothing that can be done to start or set up the device. This behaviour ensures the safety of the device and deters theft.