Click on Automatic Logon and apply enter password.
Go back to Settings then go back User Manager and doesn’t stick.
As reboot and get Logon Screen.
Something to do with SDDM? as just switched to that from default.
Tho used SDDM in other Plasma 5 distro’s and didn’t have this issue.
Confused by the empty password box? For email? as clicking on it brings up new password? confusing.