Aeonitis

Message of Issue: "Screen overlay detected - To change this permission setting you first have to turn off the screen overlay from Settings > Apps"

Scope of issue: This only applies to Android M (6.0/API v23) Or Over

Explanation: Other apps installed on the users device may be utilizing a screen overlay on your phone (e.g. Twilight, Red Moon, etc...)
Screen overlays are virtual layers that cover part or all of screen while another app is in the foreground. 
It may be dangerous for android to allow you to to change a sensitive setting while an overlay is active because you may prone to 'tap-jacking'
(i.e. a malicious application displays a fake user interface that seems like it can be interacted with, but actually passes interaction events such as finger taps to a hidden user interface behind it.).
Therefore to improve security, android doesn't allow you to change sensitive settings while an active overlay is detected, unless the user permits the app to do so. 
Source: https://commonsware.com/blog/2016/03/24/