Nvidia Drivers – Fix Disconnected Monitors on Second GPU in Ubuntu 18.04

I'm setting up a workstation with 2 GPU (Nvidia GTX1050 Ti) and 6 displays (samsung md230x6).

It's all working fine except that the desktop shows only on the displays of the first GPU; the other three are black: I cannot move any window upon but the mouse cursor actually shows as a black cross with white outline.

Funny fact is that I can actually change the color of the black screens via nvidia-settigs GUI Color Correction.

Seem the same issue as in 3rd monitor showing "X" cursor.

nvidia-smi:

$ nvidia-smi
+-----------------------------------------------------------------------------+
| NVIDIA-SMI 396.54                 Driver Version: 396.54                    |
|-------------------------------+----------------------+----------------------+
| GPU  Name        Persistence-M| Bus-Id        Disp.A | Volatile Uncorr. ECC |
| Fan  Temp  Perf  Pwr:Usage/Cap|         Memory-Usage | GPU-Util  Compute M. |
|===============================+======================+======================|
|   0  GeForce GTX 105...  Off  | 00000000:01:00.0  On |                  N/A |
|  0%   46C    P8    N/A / 120W |    624MiB /  4037MiB |      1%      Default |
+-------------------------------+----------------------+----------------------+
|   1  GeForce GTX 105...  Off  | 00000000:02:00.0  On |                  N/A |
| 45%   29C    P0    N/A /  75W |     64MiB /  4040MiB |      0%      Default |
+-------------------------------+----------------------+----------------------+

+-----------------------------------------------------------------------------+
| Processes:                                                       GPU Memory |
|  GPU       PID   Type   Process name                             Usage      |
|=============================================================================|
|    0       953      G   /usr/lib/xorg/Xorg                            34MiB |
|    0      1003      G   /usr/bin/gnome-shell                          48MiB |
|    0      1250      G   /usr/lib/xorg/Xorg                           286MiB |
|    0      1393      G   /usr/bin/gnome-shell                         147MiB |
|    0      2355      G   ...-token=C398224CE3FA660C9FF3A88B97994567   105MiB |
|    1       953      G   /usr/lib/xorg/Xorg                            30MiB |
|    1      1250      G   /usr/lib/xorg/Xorg                            31MiB |
+-----------------------------------------------------------------------------+

xrandr:

$ xrandr
 Screen 0: minimum 8 x 8, current 5760 x 1080, maximum 32767 x 32767
 DVI-D-0 connected primary 1920x1080+0+0 (normal left inverted right x axis y axis) 510mm x 287mm
    1920x1080     60.00*+  50.00  
    ...
 HDMI-0 disconnected (normal left inverted right x axis y axis)
 DP-0 connected 1920x1080+1920+0 (normal left inverted right x axis y axis) 510mm x 278mm
    1920x1080     60.00*+  59.94    50.00  
    ...
 DP-1 disconnected (normal left inverted right x axis y axis)
 HDMI-1 disconnected (normal left inverted right x axis y axis)
 HDMI-2 connected 1920x1080+3840+0 (normal left inverted right x axis y axis) 510mm x 287mm
    1920x1080     60.00*+  50.00  
    ...

kernel:

$ uname -a
Linux myhostname 4.15.0-33-generic #36-Ubuntu SMP Wed Aug 15 16:00:05 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux

lspci:

$ lspci | grep VGA
01:00.0 VGA compatible controller: NVIDIA Corporation GP107 [GeForce GTX 1050 Ti] (rev a1)
02:00.0 VGA compatible controller: NVIDIA Corporation GP107 [GeForce GTX 1050 Ti] (rev a1)

/usr/share/X11/xorg.conf.d/10-nvidia.conf:

Section "OutputClass"
    Identifier "nvidia"
    MatchDriver "nvidia-drm"
    Driver "nvidia"
    Option "AllowEmptyInitialConfiguration"
    ModulePath "/usr/lib/x86_64-linux-gnu/nvidia/xorg"
EndSection

/etc/X11/xorg.conf

/var/log/Xorg.log

Update:

Turns out it is not possible to extend the desktop to the 6 monitors with the proprietary driver and two cards. Thanks to Generix for the answers.

So I'm trying with Nouveau but for now I'm stuck in the notorius login loop… [to be continued]