compare these three pictures.Seems like the screen's pcb has something to do with the issue.I think that supports "bad gluing theory"
Can you give a photo. My mate 20 no screen problem.
In the first picture the defect is exagerated , the second one is a iphone XR wich seems to have the same problem and the third is the mate 20 original picture.
I found this:
unfortunately, the pics aren't that good.I cannot see if the screen and the digitizer are glued together.
I managed to reproduce the issue : when I make a bug report from develloper option while listening to music.Bluetooth seems unaffected.I made a video of the problem: https://www.youtube.com/watch?v=6XZSef6fuKU
In france ,just ordered!