Screen goes black, freezes for a few seconds before computer turns off

[sifr01]

This issue seems to have arisen since I upgraded from 4.5.33 to kernel 4.9.59.
It is a reasonably fresh install of SGOS. A memtest shows no errors. The error still occurs with laptop battery out and wifi off. I have been looking back at syslog each time the crash has occurred and cant isolate any specific log entries which I think point to the problem except:
subgraph kernel: [ 738.893976] (etc etc) ERROR CPU pipe A FIFO underrun
subgraph kernel: [ 738.893991] (etc etc) ERROR PCH transcoder A FIFO underrun

This bug tracker reported the same issue, suggested the bug was kernel-related and also had a symptomatic black screen:
https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1695989

There is also repeated grsec error messages but I am not sure if it is grsec that is killing gdm or Xorg that is the problem:
subgraph kernel: [ 41.624730] grsec: denied resource overstep by requesting 2048 for RLIMIT_NOFILE against limit 1024 for /usr/lib/xorg/Xorg/[Xorg:948] uid/euid:1000/1000 gid/egid:1000/1000, parent /usr/lib/gdm3/gdm-x-session[gdm-x-session:946] uid/euid:1000/1000 gid/egid:1000/1000

I have tried:
$ulimit -n 2048 to resolve this issue

[sifr01]

Modifications I have made that might be factors?:
I have a swap partition encrypted with a random password each time on boot. But syslog hasnt mentioned any issues in relation to it.
I have added a few rules to the ferm.conf firewall