This is actually a bug. I've
been seeing this myself and it appears I am not alone.
Rebooting is just a workaround that fixes this _sometimes_ and
its sheer luck, due to a race condition. The issue seems to be
affecting other distro's too and seems to be due to a stale
/run/nologin file being left lingering after boot, making
login impossible. So its not really solved at all until the
underlying race condition (bug) gets fixed.
If you ctrl-alt-f1 and login as root and remove /run/nologin
all will be well (for a little while).
Please see the following links where its explained in more
detail:
https://bugzilla.opensuse.org/show_bug.cgi?id=980324
Bug filed with systemd author:
https://github.com/systemd/systemd/issues/3436