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If you are taking about the Always On Display, then you are not alone. Lately, I have noticed the same thing, although I can't say for sure exactly when during the night it happens. I put the phone on the charger and the AOD is displaying fine. But, if I wake up before my alarm goes off, the phone display is completely black. That is annoying, as I'd like to see the time without having to wake the phone.
its the night edge always on i noticed last night that it was coming and going whenever it pleases obviously its a bug.