I was having the same issue with WiFi, and this is how I cleared it up. If I missed a similar answer in this thread I apologize.
Before I go to bed I would turn off the WiFi and data network on my phone so as not to be disturbed by email notifications at 2am. Recently I've noticed that my WiFi is ON when I get up, that is if I hadn't already been awakened in the middle of the night by email being received.
It took a a few days to realize the culprit in this case was the Xfinity WiFi App I had installed. In the settings for the app I found a prompt to "Turn on WiFi when in range", and it was checked by default.
I have a powerful Xfinity connection close to my house, so close that often when I do turn on WiFi it connects to that and not my home WiFi. I think that during the night the signal is being picked up by my phone (I'm not sure at this point if the phone is ALWAYS listening, even when off, or the app allows listening regardless of WiFi status) and turning on the WiFi.
** edit: It appears I didn't see the post immediately prior to mine, again I apologize.