TFA and your blog post both mention SLiM as a login manager, according to the Arch wiki[0]:
"The SliM project has been abandoned (the project homepage is down, leaving a github mirror), and is not fully compatible to systemd, including logind sessions. Consider using a different Display manager or Xinitrc."
"The SliM project has been abandoned (the project homepage is down, leaving a github mirror), and is not fully compatible to systemd, including logind sessions. Consider using a different Display manager or Xinitrc."
Lightdm [1] seems to be a better alternative.
[0] https://wiki.archlinux.org/index.php/SLiM [1] https://wiki.archlinux.org/index.php/LightDM