Just had my Spectre evaluated (see link for my original post/problem)
https://h30434.www3.hp.com/t5/Notebook-Video-Display-and-Touch/Vertical-Lines-on-my-HP-Spectre-x360-...
The tech pinpointed the problem to a visibly worn out monitor connecting cable which he attributes to the 360 hinge (although I have rarely used the laptop in tablet mode/flipped). Damage to the screen seems permanent however.
Not sure if that's all there is to the story, but it would at least explain why so many people are reporting the problem across different models with the hinge.