$ xrandr 
Screen 0: minimum 8 x 8, current 1920 x 1080, maximum 32767 x 32767
DP1 disconnected (normal left inverted right x axis y axis)
HDMI1 connected 1920x1080+0+0 (normal left inverted right x axis y axis) 600mm x 340mm
   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  
   1280x960      60.00  
   1280x800      59.91  
   1152x864      75.00  
   1280x720      60.00    50.00    59.94  
   1024x768      75.03    60.00  
   1024x576      59.97  
   832x624       74.55  
   800x600       75.00    60.32  
   720x576       50.00  
   720x576i      50.00  
   720x480       60.00    59.94  
   720x480i      60.00    59.94  
   640x480       75.00    60.00    59.94  
   720x400       70.08  
VIRTUAL1 disconnected (normal left inverted right x axis y axis)


$ XFSETTINGSD_DEBUG=1 xfsettingsd --replace --no-daemon
xfce4-settings(displays): RRScreenChangeNotify event received.
xfce4-settings(displays): Refreshing RandR cache.
xfce4-settings(displays): Detected CRTC 63.
xfce4-settings(displays): Detected CRTC 64.
xfce4-settings(displays): Detected CRTC 65.
xfce4-settings(displays): Noutput: before = 1, after = 0.
xfce4-settings(displays): Output disconnected: HDMI1
xfce4-settings(displays): Disabling CRTC 63.
xfce4-settings(displays): No active output anymore! Attempting to re-enable the internal output.
xfce4-settings(displays): RRScreenChangeNotify event received.
xfce4-settings(displays): Refreshing RandR cache.
xfce4-settings(displays): Detected CRTC 63.
xfce4-settings(displays): Detected CRTC 64.
xfce4-settings(displays): Detected CRTC 65.
xfce4-settings(displays): Noutput: before = 0, after = 0.
xfce4-settings(displays): RRScreenChangeNotify event received.
xfce4-settings(displays): Refreshing RandR cache.
xfce4-settings(displays): Detected CRTC 63.
xfce4-settings(displays): Detected CRTC 64.
xfce4-settings(displays): Detected CRTC 65.
xfce4-settings(displays): Detected output 67 HDMI1.
xfce4-settings(displays): Noutput: before = 0, after = 1.
xfce4-settings(displays): New output connected: HDMI1
xfce4-settings(displays): enabling crtc for HDMI1
xfce4-settings(displays): CRTC 63 assigned to HDMI1.
xfce4-settings(displays): CRTC 63, output list[0] -> 67.
xfce4-settings(displays): Normalized CRTC 63: size=1920x1080, pos=0x0.
xfce4-settings(displays): min_h = 8, min_w = 8, max_h = 32767, max_w = 32767, prev_h = 1080, prev_w = 1920, prev_hmm = 286, prev_wmm = 508, h = 1080, w = 1920, hmm = 286, wmm = 508.
xfce4-settings(displays): Configuring CRTC 63.
xfce4-settings(displays): Applying changes to CRTC 63.
xfce4-settings(displays): Configuring CRTC 64.
xfce4-settings(displays): Configuring CRTC 65.
xfce4-settings(displays): RRScreenChangeNotify event received.
xfce4-settings(displays): Refreshing RandR cache.
xfce4-settings(displays): Detected CRTC 63.
xfce4-settings(displays): Detected CRTC 64.
xfce4-settings(displays): Detected CRTC 65.
xfce4-settings(displays): Detected output 67 HDMI1.
xfce4-settings(displays): Noutput: before = 1, after = 1.




xfce4-settings(displays): RRScreenChangeNotify event received.
xfce4-settings(displays): Refreshing RandR cache.
xfce4-settings(displays): Detected CRTC 63.
xfce4-settings(displays): Detected CRTC 64.
xfce4-settings(displays): Detected CRTC 65.
xfce4-settings(displays): Noutput: before = 1, after = 0.
xfce4-settings(displays): Output disconnected: HDMI1
xfce4-settings(displays): Disabling CRTC 63.
xfce4-settings(displays): No active output anymore! Attempting to re-enable the internal output.
xfce4-settings(displays): RRScreenChangeNotify event received.
xfce4-settings(displays): Refreshing RandR cache.
xfce4-settings(displays): Detected CRTC 63.
xfce4-settings(displays): Detected CRTC 64.
xfce4-settings(displays): Detected CRTC 65.
xfce4-settings(displays): Noutput: before = 0, after = 0.
xfce4-settings(displays): RRScreenChangeNotify event received.
xfce4-settings(displays): Refreshing RandR cache.
xfce4-settings(displays): Detected CRTC 63.
xfce4-settings(displays): Detected CRTC 64.
xfce4-settings(displays): Detected CRTC 65.
xfce4-settings(displays): Detected output 67 HDMI1.
xfce4-settings(displays): Noutput: before = 0, after = 1.
xfce4-settings(displays): New output connected: HDMI1
xfce4-settings(displays): CRTC 63 must be temporarily disabled.
xfce4-settings(displays): Disabling CRTC 63.
xfce4-settings(displays): min_h = 8, min_w = 8, max_h = 32767, max_w = 32767, prev_h = 1080, prev_w = 1920, prev_hmm = 286, prev_wmm = 508, h = 0, w = 0, hmm = 0, wmm = 0.
xfce4-settings(displays): Configuring CRTC 63.
xfce4-settings(displays): Configuring CRTC 64.
xfce4-settings(displays): Configuring CRTC 65.
xfce4-settings(displays): RRScreenChangeNotify event received.
xfce4-settings(displays): Refreshing RandR cache.
xfce4-settings(displays): Detected CRTC 63.
xfce4-settings(displays): Detected CRTC 64.
xfce4-settings(displays): Detected CRTC 65.
xfce4-settings(displays): Detected output 67 HDMI1.
xfce4-settings(displays): Noutput: before = 1, after = 1.
xfce4-settings(displays): RRScreenChangeNotify event received.
xfce4-settings(displays): Refreshing RandR cache.
xfce4-settings(displays): Detected CRTC 63.
xfce4-settings(displays): Detected CRTC 64.
xfce4-settings(displays): Detected CRTC 65.
xfce4-settings(displays): Detected output 67 HDMI1.
xfce4-settings(displays): Noutput: before = 1, after = 1.