I'm using multiple monitors.
When logged in everything is fine: The left monitor is positioned to the left and the right monitor is positioned to the right, but before I log in, the login-screen positions them the other way around.
This is also the position presented by bios and then the grub menu.
I don't mind where the login is displayed, but when moving the mouse, the boundary is the wrong way around and that's annoying.
Best Answer
I was experiencing this too. So long as you have your monitors configured as you want them in your user space then you should be able to follow these steps to set your monitors up the same way on the log in screen:
sudo cp ~/.config/monitors.xml /var/lib/lightdm/.config/
Kudos goes to this post over here for pointing me in the right direction: Wrong Login Screen Resolution