Comment 9 for bug 1907107

You can reproduce with that minimal user-data config

#cloud-config
autoinstall:
  version: 1
  packages:
    - lightdm
  locale: fr_FR.UTF-8
  user-data:
    timezone: Europe/Paris
  refresh-installer:
    update: yes
  identity:
    hostname: localhost
    username: first
    password: changeme

After first reboot, lightdm start without locale and with wrong timezone.
If i switch to another tty, then i can see cloud-config running, messing up tty login prompt.
Check screenshot attached, you can see at the top login prompt.