Comment 1 for bug 1570197

I've seem this happen to. I'll have to switch to a virtual terminal, run "sudo systemctl restart lightdm" to get the display back (of course, if CTL-ALT-BS wasn't disabled now by default in window managers, this fix would require fewer keystrokes).

This might be an issue with the nVidia driver as I've seen screen blanking screw up any session. While the window manager recognizes some key strokes. The biggest issue here is there is no way for the user to configure LightDM screen blanking options without editing a text file.

We'll want to get more input here to se if it is a Nvidia driver issue or a generic issue with screen blanking in Linux

System specs for refrence:
01:00.0 VGA compatible controller: NVIDIA Corporation GM206 [GeForce GTX 960] (rev a1)
AMD FX(tm)-8350 Eight-Core Processor

Relevant packages:
liblightdm-gobject-1-0/bionic,now 1.26.0-0ubuntu1 amd64 [installed,automatic]
lightdm/bionic,now 1.26.0-0ubuntu1 amd64 [installed,automatic]
lightdm-gtk-greeter/bionic,now 2.0.5-0ubuntu1 amd64 [installed,automatic]
lightdm-gtk-greeter-settings/bionic,bionic,now 1.2.2-1 all [installed,automatic]

libnvidia-cfg1-390/bionic-updates,bionic-security,now 390.116-0ubuntu0.18.04.1 amd64 [installed]
libnvidia-common-390/bionic-updates,bionic-updates,bionic-security,bionic-security,now 390.116-0ubuntu0.18.04.1 all [installed]
libnvidia-compute-390/bionic-updates,bionic-security,now 390.116-0ubuntu0.18.04.1 amd64 [installed]
libnvidia-decode-390/bionic-updates,bionic-security,now 390.116-0ubuntu0.18.04.1 amd64 [installed]
libnvidia-encode-390/bionic-updates,bionic-security,now 390.116-0ubuntu0.18.04.1 amd64 [installed]
libnvidia-fbc1-390/bionic-updates,bionic-security,now 390.116-0ubuntu0.18.04.1 amd64 [installed]
libnvidia-gl-390/bionic-updates,bionic-security,now 390.116-0ubuntu0.18.04.1 amd64 [installed]
libnvidia-ifr1-390/bionic-updates,bionic-security,now 390.116-0ubuntu0.18.04.1 amd64 [installed]
nvidia-compute-utils-390/bionic-updates,bionic-security,now 390.116-0ubuntu0.18.04.1 amd64 [installed]
nvidia-dkms-390/bionic-updates,bionic-security,now 390.116-0ubuntu0.18.04.1 amd64 [installed]
nvidia-driver-390/bionic-updates,bionic-security,now 390.116-0ubuntu0.18.04.1 amd64 [installed]
nvidia-kernel-common-390/bionic-updates,bionic-security,now 390.116-0ubuntu0.18.04.1 amd64 [installed]
nvidia-kernel-source-390/bionic-updates,bionic-security,now 390.116-0ubuntu0.18.04.1 amd64 [installed,automatic]
nvidia-prime/bionic-updates,bionic-updates,now 0.8.8.2 all [installed]
nvidia-settings/bionic-updates,now 390.77-0ubuntu0.18.04.1 amd64 [installed]
nvidia-utils-390/bionic-updates,bionic-security,now 390.116-0ubuntu0.18.04.1 amd64 [installed,automatic]
xserver-xorg-video-nvidia-390/bionic-updates,bionic-security,now 390.116-0ubuntu0.18.04.1 amd64 [installed,automatic]