unable to restart lightdm after 2 weeks of no interaction

[Stefan Helmert]

System was running without problems for a long time. After two weeks of no interaction with mouse or keyboard, System did not respond on keyboard or mouse interaction anymore. Gui works (tried with DISPLAY=:1 xmessage "test" from ssh), mouse and keyboard are also working (Fn-LED or mouse cursor) but clicking and typing does not do anything.

ProblemType: Bug
DistroRelease: Ubuntu 17.10
Package: lightdm 1.24.0-0ubuntu1
ProcVersionSignature: Ubuntu 4.13.0-45.50-generic 4.13.16
Uname: Linux 4.13.0-45-generic x86_64
NonfreeKernelModules: zfs zunicode zavl zcommon znvpair nvidia_uvm nvidia_drm nvidia_modeset nvidia
ApportVersion: 2.20.7-0ubuntu3.9
Architecture: amd64
Date: Mon Aug 20 17:13:40 2018
InstallationDate: Installed on 2017-09-19 (335 days ago)
InstallationMedia: Ubuntu-Server 17.04 "Zesty Zapus" - Release amd64 (20170412)
ProcEnviron:
 TERM=xterm-256color
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=de_DE.UTF-8
 SHELL=/bin/bash
SourcePackage: lightdm
UpgradeStatus: Upgraded to artful on 2018-05-15 (96 days ago)