Hi. could be the blue light filter. mines in the pull down menu but I think you can find it in settings and display. I have it set from sunset to sunrise but can be set to any time you want ( or turned off). hope this helps.
I have these on my Phone.well only one now since I turned one off. i got them from the goodlock 2018 app. they are programmable keys for gestures. I find them useful but like I said you can disable one or both if you want.
I'm having the same issue here. just changed phone to note 9 and thought it was some problem with that. I'm kind of happy it's not now 😀. Hope it's fixed soon.