This was 2 weeks ago and dude who discovered it thought it was a feature - https://forums.developer.apple.com/thread/79235 (scroll to bottom of page)
chethan177 Nov 13, 2017 12:48 PM (in response to Taylor E) Note: This solution might be specific to High Sierra
Try this: Solution 1: On startup, click on "Other" Enter username: root and leave the password empty. Press enter. (Try twice) If you're able to log in (hurray, you're the admin now), then head over to System Preferences>Users & Groups and create a new Admin account. Now restart and login to the new Admin Account (you may need a new Apple Id). Once you're logged into this new Admin Id, you can again proceed to your System Preferences>Users & Groups. Open the Lock Icon with your new Admin ID/Password. Assign "Allow user to administer this computer" to your original Apple ID. Restart.