Hi, are you using "Display Preferences" or "xrandr" to make the right monitor as primary ?
I also tried that methods but I don't find any "primary' indicator in "Display Preferences" GUI. so I tried "xrandr" but it seems that it always select monitor under (0,0) as primary monitor so you will see "it always defaults to the left monitor as the primary".
could you please tell me what's your approach to achieve "primary" so I can make a try ?