I mean, I only tried 15 times, I don't know if that counts as "several" but this doesn't work for me.

It looks to me like my root user is disabled.

When I type "root" into the username field and click unlock (in System Preferences > Users & Groups) "root" is replaced with my username and the dialog shakes... I have to type root in each time, but it never unlocks. 10.13.1

Edit: trying it after logging out keeps "root" in the username field, but never logs me in... tried 20+ times