If I try to switch to a virtual console by Ctrl-Alt-F1 or greater (up to Ctrl-Alt-F6), screen is black. But I can return by Ctrl-Alt-F7 (if light-locker is not used; update: now I can return even if light-locker is used).
This happens with nvidia-340 driver (I am using version 340.107-0ubuntu0.18.04.1 from bionic-updates), but not with nouveau driver. With nouveau driver I can switch to TTY2, TTY3 and TTY6 for text console, and TTY7 gives the X session.
This bug also breaks light-locker, switching user and maybe something else.
ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: light-locker 1.8.0-1ubuntu1
ProcVersionSignature: Ubuntu 4.18.0-13.14~18.04.1-generic 4.18.17
Uname: Linux 4.18.0-13-generic x86_64
NonfreeKernelModules: wl nvidia
ApportVersion: 2.20.9-0ubuntu7.5
Architecture: amd64
CurrentDesktop: XFCE
Date: Fri Jan 11 16:17:15 2019
EcryptfsInUse: Yes
InstallationDate: Installed on 2017-01-05 (735 days ago)
InstallationMedia: Xubuntu 16.04.1 LTS "Xenial Xerus" - Release amd64 (20160719)
SourcePackage: light-locker
UpgradeStatus: No upgrade log present (probably fresh install)
According to your bug description, this it not a bug in light-locker.
Is it a new problem that appeared after a kernel or nvidia driver update?