I have found using the new lock screen function on the Apple menu will return to the login screen as I would expect, but a few seconds later the screen will go to black and go to sleep. The keyboard backlight also goes off. This is happing on a 2013 13" MacBook Pro and a 2012 iMac. But this doesn't happen on a 2010 Mac Pro (it will sit at the login identifiably)... Power settings shouldn't be coming into play, they are fully disabled on the iMac and Mac Pro, and disabled when on A/C power for the MacBook... Before High Sierra I used the "login screen" option from the fast user switching menu. When using this option, the screen doesn't go to sleep. I like the lock screen as it is engaged immediately, unlike the fast user switching menu option with kicks in after several seconds... Anyone else have a similar experience with the lock screen function?