Upgrading from 16.04 to 18.04 on 32bit I observe that I remain with the same LightDM login instead of the new Slick Greeter one. Try on second system, same issue.
To solve this:
- go in folder “/usr/share/lightdm/lightdm.conf.d”
- and delete the "60-lightdm-gtk-greeter.conf "as it was not removed on install and it will overide configuration in already created file “50-slick-greeter.conf”
Welcome to the forum @mircea , and thank you for the solution.