P4317Q, Ubuntu issue

Hi,

my P4317Q runs without a problem on Windows 10. But on Ubuntu 16.04, it only works if I mirror the displays of my Precision M4700 and the P4317Q. If I don't mirror them, I get the message "No DP signal from your device" on the P4317Q. My laptop is connected to the P4317Q via the video 2 output of a PR02X docking station. 

Does anyone know how to fix this problem?

Edit: I found out that my screen works if I attach it directly to my laptop. Nevertheless, since I want to operate more than one screen and I had the same problem with a 27 inch Dell screen in the past, I still need to resolve the issue.