Ubuntu 18.04 MSI GS65 HDMI output not always detected

Hardware

• MSI GS-65-053 Stealth Thin 8RF
• GeForce GTX 1070
• LG 43UD79 Display

Software

• Ubuntu 18.04
• Nvidia 415.27 driver

What I've Already Tried

• switching from gdm3 to lightdm
• re-installing nvidia drivers
• trying different display, different HDMI cables

Description

After installing Ubuntu 18 on my MSI, the HDMI output for my LG external monitor was not detected. Initial searching got me a 'solution': to switch display manager from gdm3 to lightdm. This worked for a while, then after a series of suspends/reboots, I returned to my external monitor and the HDMI was once again not detected.

Here's the output of xrandr while connected to the LG via HDMI:

Screen 0: minimum 8 x 8, current 1920 x 1080, maximum 32767 x 32767
HDMI-0 disconnected (normal left inverted right x axis y axis)
DP-0 disconnected (normal left inverted right x axis y axis)
DP-1 disconnected (normal left inverted right x axis y axis)
eDP-1-1 connected primary 1920x1080+0+0 (normal left inverted right x axis y axis) 344mm x 193mm
   1920x1080    144.03*+  60.08    60.01    59.97    59.96    59.93  
   1680x1050     84.94    74.89    69.88    59.95    59.88  
   1600x1024     60.17  
   1400x1050     85.00    74.76    70.00    59.98  
   1600x900      59.99    59.94    59.95    59.82  
   1280x1024     85.02    75.02    60.02  
   1440x900      59.89  
   1400x900      59.96    59.88  
   1280x960      85.00    60.00  
   1440x810      60.00    59.97  
   1368x768      59.88    59.85  
   1360x768      59.80    59.96  
   1280x800      59.99    59.97    59.81    59.91  
   1152x864     100.00    85.06    85.00    75.00    75.00    70.00    60.00  
   1280x720      60.00    59.99    59.86    59.74  
   1024x768      85.00    75.05    60.04    85.00    75.03    70.07    60.00  
   1024x768i     86.96  
   960x720       85.00    75.00    60.00  
   928x696       75.00    60.05  
   896x672       75.05    60.01  
   1024x576      59.95    59.96    59.90    59.82  
   960x600       59.93    60.00  
   832x624       74.55  
   960x540       59.96    59.99    59.63    59.82  
   800x600       85.00    75.00    70.00    65.00    60.00    85.14    72.19    75.00    60.32    56.25  
   840x525       85.02    74.96    69.88    60.01    59.88  
   864x486       59.92    59.57  
   800x512       60.17  
   700x525       85.08    74.76    70.06    59.98  
   800x450       59.95    59.82  
   640x512       85.02    75.02    60.02  
   720x450       59.89  
   700x450       59.96    59.88  
   640x480       85.09    60.00    85.01    72.81    75.00    59.94  
   720x405       59.51    58.99  
   720x400       85.04  
   684x384       59.88    59.85  
   680x384       59.80    59.96  
   640x400       59.88    59.98    85.08  
   576x432      100.11    85.15    85.09    75.00    75.00    70.00    60.06  
   640x360       59.86    59.83    59.84    59.32  
   640x350       85.08  
   512x384       85.00    75.03    70.07    60.00  
   512x384i      87.06  
   512x288       60.00    59.92  
   416x312       74.66  
   480x270       59.63    59.82  
   400x300       85.27    72.19    75.12    60.32    56.34  
   432x243       59.92    59.57  
   320x240       85.18    72.81    75.00    60.05  
   360x202       59.51    59.13  
   360x200       85.04  
   320x200       85.27  
   320x180       59.84    59.32  
   320x175       85.27  
DP-1-1 disconnected (normal left inverted right x axis y axis)
HDMI-1-1 disconnected (normal left inverted right x axis y axis)

Edit 1:

To clarify: I experienced the same outcome regardless of monitor or cable used. Also tried HDMI-HDMI, HDMI-DVI, HDMI-DP. The external monitor connection was not detected in any of these cases.