SDDM scaling issue with 410/415 Nvidia drivers on Kubuntu 18.10

I have a laptop(ASUS ZenBook Pro UX550VD) with both Intel and GeForce GTX 1050 graphics card with an extra 2560x1440 monitor connected with thunderbolt converted to HDMI.

SDDM displays the login screen with 2560x1440 on both monitors(laptop monitor is only 1920x1080). After a lot of things I tried online it seems the issue is with /sbin/prime-offload but I’m not sure how to fix it.

  • I don't have a default xorg.conf and whenever I create one(manually or with nvidia-xconfig) I get a black screen.
  • Plasma is running correctly with two monitors only SDDM has issue.

nvidia-bug-report.log.gz (1000 KB)

Sounds like a sddm issue. If you switch to intel only, does the scaling issue still happen?

I didn’t try with Intel but with 4.19.* kernel and Nvidia driver 390 works properly. But downgrading kernel or updating the driver breaks it again(4.18.* Canonical kernel + 390 driver is not working).

Because of this I don’t think it’s sddm issue.