What's the router brand? I'm guessing, since you said you changed it in advanced settings, you chose 'never' in the keep wifi on while sleep tab?
I'm still leaning toward an app keeping this on.
Maybe gps or an apps location function is enabled.
Does your advanced screen look like the above poster, or do you also have a wifi timer option?
If not maybe this app could help.
https://forums.androidcentral.com/e?...token=2mp4GknS
Posted via TriForced Sprint GS4