Logout in the dark of the night

During the dark of the night the following message appeared in my
syslog.

Dec 27 01:27:16 mycomputer sshd(pam_unix)[25585]: session closed for
user robert
Dec 27 01:27:16 mycomputer sshd[25579]: syslogin_perform_logout:
logout() returned an
error

I've never seen it before. I was sound asleep at the time.

I was not logged in from any terminal and had no screen sessions
running.

I don't have any timeouts set.

Are there dark forces operating?

Or is there a mundane explanation?

.