I can only get one of the display ports on a brand new Z2 mini to work. The machine has three Display port outputs, but only the monitor connected to the lower port is working.
There are two equal monitor connected using a Display port cable each.
I have tested both monitors and cables connected to the lower Display port, and when connected to it, they work fine, so I can rule out any problem with the monitors or Display port cables.
Windows can not detect the screen connected to either of the two upper Display ports, I have also tried a Display port to DVI cable, but that did't help.
The machine is running Intel UHD630 graphics, and I have tried to update the driver to latest version: 25.20.100.6374
I also flashed the BIOS to Q50 Ver. 01.04.07 - 01/31/2019. (The machine shipped with BIOS 01.04.01).
I also tried to boot Ubuntu Live from a USB drive, and Ubuntu could not detect more than the screen connected to the lower port either.
On the HP web page, it states that the machine should have two Display port outputs: