Battery drain: Screen consuming battery when the phone is sleeping

A

AC Question

Can someone help me figure out the issue I've been experiencing with my Galaxy Note 5? I'm on AT&T, all updates installed, not rooted. The phone is new, but I've been getting a lot of battery drain. I have the beta version of Greenify installed and aggressive Doze turned on; I use ShutApp whenever too many apps are running in the background. My screen brightness is controlled by Lux, and usually set at very low %.
I'm using GSAM to track the battery consumption, but I don't believe it's catching everything. The stock battery details is showing the screen as the main contributor to the battery drain, and the graph is steadily declining even when the screen is turned off. GSAM shows that the screen is consuming battery when it's turned off.
How is that possible?
I'll try to post some screenshots next