3rd monitor disabled

[falsobuio]

Hello to all,
I have a 3rd monitor through the VGA port and it fails to show the gnome desktop after the login. At the login screen it is in normally in use (grey backroung and mouse is visible on it).
My setup is on a laptop. 1st monitor (laptop built-in), 2nd HDMI, 3rd VGA (disabled).

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Operating System: Debian GNU/Linux 9 (stretch)
Kernel: Linux 4.9.0-5-amd64
Architecture: x86-64

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01:00.0 VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI] Thames [Radeon HD 7500M/7600M Series]

xrandr gives me:

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root@falsodebian:~# xrandr
Screen 0: minimum 320 x 200, current 3286 x 1080, maximum 16384 x 16384
LVDS connected primary 1366x768+1920+312 (normal left inverted right x axis y axis) 0mm x 0mm
   1366x768      60.02*+
   1280x720      59.86  
   1152x768      59.78  
   1024x768      59.92  
   800x600       59.86  
   848x480       59.66  
   720x480       59.71  
   640x480       59.38  
HDMI-0 connected 1920x1080+0+0 (normal left inverted right x axis y axis) 160mm x 90mm
   1920x1080     60.00 +  50.00    59.94* 
   1920x1080i    60.00    50.00    59.94  
   1680x1050     59.88  
   1600x900      60.00  
   1280x1024     75.02    60.02  
   1440x900      59.90  
   1366x768      59.79  
   1280x800      59.91  
   1152x864      75.00  
   1280x720      60.00    50.00    59.94  
   1024x768      75.03    70.07    60.00  
   832x624       74.55  
   800x600       72.19    75.00    60.32  
   720x576       50.00  
   720x480       60.00    59.94  
   640x480       75.00    72.81    66.67    60.00    59.94  
   720x400       70.08  
VGA-0 connected (normal left inverted right x axis y axis)
   1920x1080     60.00 +
   1680x1050     59.95  
   1400x1050     59.98  
   1600x900      60.00  
   1280x1024     75.02    60.02  
   1440x900      59.89  
   1280x800      59.81  
   1152x864      75.00  
   1280x720      60.00  
   1024x768      75.03    60.00  
   800x600       75.00    60.32  
   640x480       75.00    59.94  
   720x400       70.08  

I have install the latest xorg

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sudo apt-get install xserver-xorg-video-ati
Reading package lists... Done
Building dependency tree       
Reading state information... Done
xserver-xorg-video-ati is already the newest version (1:7.8.0-1+b1).

When i am trying to disconnect, change, alter the resolutions etc gnome stucks and is not responding. I have to do a hard reset.

On linux mint these monitors work fine.

Any suggestions?

Thanks a lot!

EDIT:
I forgot to mention that my HDMI input is getting signal from an HDMI splitter
https://www.amazon.co.uk/gp/product/B01 ... TF8&psc=1 HDMI Splitter, SOWTECH 2 Way HDMI Splitter with 1 Input to 2 Outputs, Support 3D Full HD 1080P HDTV

When HDMI monitor is directly connected to laptop, all 3 monitors work fine. When the splitter is in use the VGA monitor (3rd one) fails to work.
It is strange that the splitter messes up the 3rd monitor that has nothing to do with what is going on at the HDMI splitter?

[bw123]

xrandr gives me:
root@falsodebian:~# xrandr
<snip>
Screen 0: minimum 320 x 200, current 3286 x 1080
<snip>
VGA-0 connected (normal left inverted right x axis y axis)

VGA-0 has no coordinates like the others, so it looks like it's not part of the current "screen" but I don't know how gnome handles this. Find a setting somewhere to enable it.

Probably not good to run xrandr as root?