Mac keeps trying to restart/log out during sleep.

Hi there.

Odd problem, have not found anything by googling. Maybe someone here can help.

iMac 5K, 10.13.3. (nothing plugged in except a keyboard and a lightning-cable, and neither are the culprit)
Whenever I put the machine to sleep for a longer time, I'm liable to come back to notice it has either rebooted or logged out the user (I come back to a login screen with all available users, not the "enter your password" -screen).

Happens recurrently (about 2/3 times when the machine's been to sleep for an hour or more), except when I leave an old software (non-autosave) with an unsaved file open. Then (when I take the computer out of sleep) I enter my password normally to find a prompt saying that the machine could not log off because of the unsaved file.

Have looked at the console, but am no expert - can't find anything which would enlighten me.

If you want, you can have a look at the console log (system) for the machine between 01:43 (when I stopped working last night and put the machine to sleep) and 09:39 (when I fired up the machine) here.

TIA & RGDS,
Pekka

 

Wow! Impressive. Did not know that was there.
Hope this settles it. Thanks,

RGDS,