Jun 25 12:40:22 localhost.localdomain systemd: Started Simple Desktop Display Manager.
Jun 25 12:40:28 localhost.localdomain sddm-helper: pam_unix(sddm-greeter:session): session opened for use r sddm by (uid=0)
Jun 25 12:40:36 asphodel sddm: Auth: sddm-helper exited with 6
I then entered: systemctl restart sddm.service and everything worked fine.
Looks like an issue with sddm-helper, whatever that is...