Debugging and Configuring Xorg with Displayport MST hub on Kubuntu

I am a (K)ubuntu newbie, so I am still getting to grips with how the desktop environment is put together.

I am currently trying to get an MST hub to work so that I can have 3 monitors connected to my Intel NUC i3-6100U on latest Kubuntu 16.04 (Plasma).

I feel like the issues I am experiencing must be configuration issues, as it seems like (K)ubuntu - or rather Xorg, if I understand things correctly - can in certain circumstances display graphics on all 3 monitors, just not reliably.

This is the setup I am attempting:

1. Primary display, Asus Ve248 connected via HDMI




2. Two Dell 2412M displays connected via a Club3d MST Displayport Hub

All connecting cables support the "new" Displayport standard.

Symptoms:

Image will display fine, mirrored on all three displays if I just connect them up and start up the machine at login screen and if I hit CTRL+Alt+F1 to go to the terminal

Once I hit the desktop however, I get no image on the MST connected displays.

If I then go into Display Configuration and enable the two MST connected displays, usually the desktop craps out - mouse cursor, any open windows and panel moves to one of the Dell screens and I have no image on the MST connected displays.

However, I do get flashes of my desktop popping up once in a while on the MST connected displays.

After a reboot my desktop on the primary HDMI display is fine, but no image on the MST connected displays, except for intermittent flashes.

In my terminal (ctr+alt+f1) I get messages which say something like ERROR CPU Pipe B (or C) FIFO Underrun

Here's output from xrandr - not sure if it helps, but anyway:

Screen 0: minimum 8 x 8, current 5760 x 1200, maximum 32767 x 32767
DP1 disconnected (normal left inverted right x axis y axis)
DP1-1 connected 1920x1200+1920+0 (normal left inverted right x axis y axis) 518mm x 324mm
   1920x1200     59.95*+
   1920x1080     60.00
   1600x1200     60.00
   1680x1050     59.95
   1280x1024     60.02
   1280x960      60.00
   1024x768      60.00
   800x600       60.32
   640x480       60.00
   720x400       70.08
DP1-2 connected 1920x1200+0+0 (normal left inverted right x axis y axis) 518mm x 324mm
   1920x1200     59.95*+
   1920x1080     60.00
   1600x1200     60.00
   1680x1050     59.95
   1280x1024     60.02
   1280x960      60.00
   1024x768      60.00
   800x600       60.32
   640x480       60.00
   720x400       70.08
HDMI1 connected primary 1920x1080+3840+0 (normal left inverted right x axis y axis) 531mm x 299mm
   1920x1080     60.00*+  50.00    59.94    59.99
   1920x1080i    60.00    50.00    59.94
   1600x1200     60.00
   1680x1050     59.88
   1280x1024     75.02    60.02
   1440x900      59.90
   1280x960      60.00
   1366x768      59.79
   1152x864      75.00
   1280x720      60.00    50.00    59.94
   1024x768      75.08    70.07    60.00
   832x624       74.55
   800x600       72.19    75.00    60.32    56.25
   720x576       50.00
   720x480       60.00    59.94
   640x480       75.00    72.81    66.67    60.00    59.94
   720x400       70.08
HDMI2 disconnected (normal left inverted right x axis y axis)
VIRTUAL1 disconnected (normal left inverted right x axis y axis)

Where should I start looking to debug this? It feels like the system is sooo close to just working right out of the box, but that there is a configuration or driver issue at work.

Any input much appreciated.