Latitude E7450 will not show 4K on external monitor

I have a Dell Latitude E7450 running win 10 that I connect to a Dell U2913WM using a HDMI cable. 

The computer used to show the correct display settings the last 10 months or so (extend the screen and use 2560 x 1080 on the external monitor) when I connect them. Since a few days however the highest possible screen resolution is 1920 on the external monitor and the computer never remembers the "extend" settings but rather use the "only use external monitor" option when they are connected.

I have updated the drivers for display, graphics card and rebooted a lot of times but still the same. I guess this is probably a Win 10 issue since its probably related to some update - but I still can't figure out how to solve this. Ideas? 

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