WORKAROUND/FIX:
1. Log in and configure your multi-monitor desktop the way you want.
2. sudo cp ~/.config/monitors.xml ~gdm/.config/
3. Edit ~gdm/.config/monitors.xml to make sure the monitor you want as primary is set as <primary>yes</primary>
4. Log out.
WORKAROUND/FIX:
1. Log in and configure your multi-monitor desktop the way you want.
2. sudo cp ~/.config/ monitors. xml ~gdm/.config/
3. Edit ~gdm/.config/ monitors. xml to make sure the monitor you want as primary is set as <primary> yes</primary>
4. Log out.