The second user cannot start their session, login screen has low resolution

[Gabor Czibula]

The first user can start their session successfully with autologin. When I try to switch to the second user, the login screen has very low resolution and it cannot start the secondary user session. I tried to change the value of the autologin user, than the other user session start well, but the original user session failed. That's why I think this is not a user related error, always the second user session fail, does not matter which one is the first user. The only differences between the default settings that passwordless login switch on the pam config and use nvidia-340 driver instead of noveau. The strange thing that this lightdm config works well with noveau driver, the problem with noveau driver that the video playing freeze the computer. Previously lightdm and nvidia driver work well on 16.04. This is a clean install not an upgrade from 16.04. I think the problem somewhere virtual X terminals handled by ligthDm.

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: lightdm 1.26.0-0ubuntu1
ProcVersionSignature: Ubuntu 4.15.0-22.24-generic 4.15.17
Uname: Linux 4.15.0-22-generic x86_64
NonfreeKernelModules: nvidia
ApportVersion: 2.20.9-0ubuntu7.1
Architecture: amd64
CurrentDesktop: X-Cinnamon
Date: Tue Jun 5 23:07:11 2018
EcryptfsInUse: Yes
InstallationDate: Installed on 2018-05-27 (9 days ago)
InstallationMedia: Ubuntu 18.04 LTS "Bionic Beaver" - Release amd64 (20180426)
SourcePackage: lightdm
UpgradeStatus: No upgrade log present (probably fresh install)
mtime.conffile..etc.pam.d.lightdm: 2018-05-27T21:23:23.664631