Yeah so it sounds like there's some hardware/driver issue. I found this forum thread, which suggests that changing the orientation of the USB-C connector (!) can fix it.
Unfortunately I don't own a PBP so I can't try to replicate the issue on my own hardware.
Edit: another potentially relevant forum post.
Unfortunately I don't own a PBP so I can't try to replicate the issue on my own hardware.
Edit: another potentially relevant forum post.