Screen resolution on external monitor at login

Hi, I'm connecting my laptop to an eGPU (Nvidia) and when the system boots up I get the login screen on both my laptop (FHD resolution) and my external screen (3440x1440). The problem is the that resolution is the same on both screen and thus only covers a portion of the external screen. After login, it's fine. So I guess it has to do with LightDM.
Any thoughts?

May be you should have to change its resolution by hand. see below.


Thanks for the reply. But the resolution after login is fine, and the monitor preferences are right. I found this is a known lightdm bug..

I'll try something suggested at the Manjaro forums.