external screen no longer support native resolution

Tue Jul 21 07:32:08 UTC 2015

Hi!

I just upgraded to F22 and my external monitor (a Koios 24" 1920x1200)
no longer works in its native resolution. I can only get 1280 x 768 to
display.

Everything was working well before. My video chip is the Intel HD
Graphics 5500 (Broadwell GT2) (the laptop is a X1 Carbon 3rd generation).

GNOME display settings does offer the native resolution but it just
doesn't work (I get an screen switched off).

How would you troubleshooting this?

Thank you.

Fred