Hello ilyaburyy,
Thank you for reporting the issue. We have confirmed that this is a bug, and it will be fixed in Server Suite 2017.
As fstonedahl pointed out, the /etc/lightdm/lightdm.conf file is not modified correctly by our postinst script. Specifically, echo -e option is missing when the script is generating the lightdm configuration file.
As a workaround, please modify the /etc/lightdm/lightdm.conf file as fstonedahl suggested:
[SeatDefaults]
greeter-show-manual-login=true
Please note that this parameter is needed to specify users when logging in through console.