GDM3 fails to start X

[dino99]

Doing some tweaks on that yakkety 64 bits running gnome-shell powered by nvidia-370 driver, i've discovered that issue.

Steps to reproduce:

- on the initial working session, run "sudo dpkg-reconfigure lightdm" and select/validate gdm3
- close the session and reboot
- as a result, X fails to start/load
- switched to ctrl+alt+F2 and reconfigure again to choose back lightdm, and reboot
- that time X start as expected

Could it be related to the lightdm/accountservice relationship, not identical in the case of gdm3 choice ?
info: https://bugs.launchpad.net/ubuntu/+source/lightdm/+bug/857651 #4

using:
lightdm (1.19.4-0ubuntu1) yakkety
lightdm-gtk-greeter (2.0.1-2ubuntu4) xenial
(purged: unity-greeter (16.10.2.2) yakkety and most of unity)

ProblemType: Bug
DistroRelease: Ubuntu 16.10
Package: gdm3 3.20.1-1ubuntu2
ProcVersionSignature: Ubuntu 4.8.0-4.5-generic 4.8.0-rc3
Uname: Linux 4.8.0-4-generic x86_64
NonfreeKernelModules: nvidia_uvm nvidia_drm nvidia_modeset nvidia
ApportVersion: 2.20.3-0ubuntu7
Architecture: amd64
CurrentDesktop: GNOME
Date: Thu Aug 25 17:03:25 2016
SourcePackage: gdm3
UpgradeStatus: No upgrade log present (probably fresh install)

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.