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I have three displays in my computer setup with two plugged with HDMI-cables and one with DisplayPort-cable. My problem is the following:

When I start my computer all the displays start and work correctly. If I lock my screen for a little while (say few minutes) and then open the lock all screen work fine. If however I lock my screens and go away for a longer time (say 15-30 mins) and then open screen lock, one display plugged with HDMI-cable does not start. Even if I try to adjust display settings nothing happens. My current fix is to restart the computer and then all the displays fire up correctly.

What could be the cause of this problem and how to fix this? I suspect it might have something to do with the system turning the screens off after few minutes. The problem is that when I try to activate the screens again one of them does not start anymore (HDMI-0).

In case you need it, here is the output of xrandr -q -command:

Screen 0: minimum 8 x 8, current 6200 x 1920, maximum 32767 x 32767
HDMI-0 connected primary 2560x1440+1080+480 (normal left inverted right x axis y axis) 608mm x 345mm
   3840x2160     30.00 +  29.97    25.00    23.98  
   2560x1440     59.95* 
   1920x1080     60.00    59.94    50.00    29.97    23.97  
   1680x1050     59.95  
   1600x900      60.00  
   1440x900      59.89  
   1280x1024     75.02    60.02  
   1280x800      59.81  
   1280x720      60.00    59.94    50.00  
   1152x864      75.00  
   1024x768      75.03    70.07    60.00  
   800x600       75.00    72.19    60.32    56.25  
   720x576       50.00  
   720x480       59.94  
   640x480       75.00    72.81    59.94  
HDMI-1 connected 1080x1920+0+0 left (normal left inverted right x axis y axis) 527mm x 296mm
   1920x1080     60.00*+  59.94    50.00    60.05    60.00    50.04  
   1600x900      60.00  
   1280x1024     75.02    60.02  
   1280x720      60.00    59.94    50.00  
   1152x864      75.00  
   1024x768      75.03    60.00  
   800x600       75.00    60.32  
   720x576       50.00  
   720x480       59.94  
   640x480       75.00    59.94    59.93  
DP-0 connected 2560x1440+3640+480 (normal left inverted right x axis y axis) 607mm x 345mm
   3840x2160     60.00 +  30.00  
   2560x1440     59.95* 
   1920x1080     60.00    59.94  
   1680x1050     59.95  
   1600x900      60.00  
   1440x900      59.89  
   1280x1024     75.02    60.02  
   1280x800      59.81  
   1280x720      60.00  
   1152x864      75.00  
   1024x768      75.03    70.07    60.00  
   800x600       75.00    72.19    60.32    56.25  
   640x480       75.00    72.81    59.94  
DP-1 disconnected (normal left inverted right x axis y axis)
DP-2 disconnected (normal left inverted right x axis y axis)
DP-3 disconnected (normal left inverted right x axis y axis)

The problem display is the one with 'HDMI-0' label.

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I found a temporary fix to this problem referencing this post:

https://bugs.launchpad.net/ubuntu/+source/xserver-xorg-video-ati/+bug/1577170

When I open up the terminal in one of my working display and type in:

gnome-screensaver-command -a

all the screens go blank, then activate them with e.g. moving mouse and now all three of them activate. So this is confirmed that it works, though it is not a really elegant long-term solution.

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