I also logged https://bugs.launchpad.net/ubuntu/+source/nvidia-graphics-drivers-340/+bug/1876551 about nvidia-340 drivers having the same problem (won't remember the config).
My workaround is a .desktop file that calls xrandr with my desired parameters I configured with nvidia tool and then dumped out with xrandr.
I also logged https:/ /bugs.launchpad .net/ubuntu/ +source/ nvidia- graphics- drivers- 340/+bug/ 1876551 about nvidia-340 drivers having the same problem (won't remember the config).
My workaround is a .desktop file that calls xrandr with my desired parameters I configured with nvidia tool and then dumped out with xrandr.