Please note that if you configure the lock screen to not allow anyone but the logged in user to unlock(preventing admin's from unlocking a user's workspace), the login field will never appear after screensaver comes on. This is a bug specific to macOS 10.15. I have not had a chance to test 10.15.1.
Command that causes issue:
security authorizationdb write system.login.screensaver authenticate-session-user
Resetting to default:
security authorizationdb write system.login.screensaver use-login-window-ui
