I share my Mac. with Mrs B, and when she wishes to use it, I "log out" so she can login. Twice now in two days the screen has locked.
From the Apple select "Log Out", the current screen (slowly sometimes) closes all the items, then (almost immediately) the login screen appears, however, the current screen has closed all the items, however, just the desktop picture is there...
From the Apple select "Log Out", the current screen (slowly sometimes) closes all the items, then (almost immediately) the login screen appears, however, the current screen has closed all the items, however, just the desktop picture is there...