Dark blue lines under screen when only exposed to sunlight (Asus zenfone max pro m2)

[Nerf_Paladin]

Good day,
I'd just noticed earlier there's a rectangular dark blue lines in my screen(under the screen) when its exposed to sunlight. It only visible when its on dark display. I even turn off the phone and it still visible. When I checked it back home there's no lines anymore and I also expose it to a light (not as bright like sunlight) and no lines is visible anymore.
I tried to checked it with .12345+= to test the display and touch, and there's no problem on it. It seems it only appears when its exposed to a bright light (sunlight)

Any Idea what is?
The picture below looks like that but its under the screen. (phone below is not mine, I just drew the line)

Thanks in advance
EDIT: some typo and additional information

[Christine_ASUS]

Hi Nerf Paladin
Thank you for your asking. If you can only recognize the frame in turn-off screen under bright sunlight, it is a normal design of the device structure and will not disturb any normal usage. You may keep your normal usage behavior.