No DisplayPort signal with D6000 on XPS 9370 with Ubuntu 18.04, nor on macOS 10.13.6

[jinnko]

Just received my D6000 today and have spent a fair bit of time trying to get the DisplayPort output working without success. Support logs attached.

- HDMI works from Ubuntu 18.04, though only at 30Hz. It does however lose signal occasionally :/
- On a Macbook Pro 13 mid 2015 model with macOS 10.13.6, HDMI sort of works, but not as a recognized display - only as a mirrored display that System Preferences isn't aware of. Similar issue on a Macbook Air, also with 10.13.6.
- Network, USB and power delivery to the XPS all seem to be working fine. Haven't tested the audio jack
- My DisplayPort cable and monitor work perfectly with my Dell DA300 mobile adapter.

I'm primarily interested in getting this working on my Ubuntu XPS laptop.

I have done the following:

- Installed the 4.2 driver from here.
- Disabled secure boot as described here.
- Configured modesetting with PageFlip disabled as described here.
- Tried increasing logging levels as described here, then connect and disconnect the DP cable from each of the two ports. No logging is emitted when the DP cable is inserted/removed.

Bottom line is I'd like to know whether the device is faulty and I should return it for a replacement.