Mate 20 lite no backlight / display issue

I noticed that in very low light situations, mostly at night (so with low screen brightness and very dark environnement), my screen does not seem to display true black. Basically I can tell if the screen is powered on or not when a true black image is being displayed. It's almost like the backlight of a LCD display. I tried to replicate the issue in the day but to no avail. What can I do?