Originally Posted by sandipt
Issue is reproduced by adding 'Option "ProbeAllGpus" "false"' in "Device" Section OR Section "Screen" for one of the GPU. Issue is not repro if Option "ProbeAllGpus" "true" for both Screens.
Confirmed. Many thanks to sandipt for informations. Now I'm able to start independent X server :1.
Working xorg.conf is in atachment.