You need to extend your 2nd display in the Windows display setting so hit F10 and select Extend or right click on your desktop, select Display Setting, scroll down until you see the Extend option in the Multiple Displays section.
I use FX4 units with Resolume almost everyday and I don't have any issues so I'm guessing your problem is coming from the cable between your server and the FX4. I'm assuming you programmed your FX4 to be 3840x2160/30 with the four HD outputs, right? Can you describe your setup including cable length?
If you look at the specs for the unit, it says: SDI Video Inputs 2 x 12Gb/s and 2 x 6Gb/s SD/HD/2K/4K. Supports single/dual/quad link 4:2:2/4:4:4. 2D/3D switchable. SDI Video Outputs 2 x 12Gb/s and 2 x 6Gb/s SD/HD/2K/4K. Supports single/dual/quad link 4:2:2/4:4:4. 2D/3D switchable. .../... Computer ...