No, it was on the table all night.. But i did get some notifications from WhatsApp.. Maybe it "woke" the doze?
Had the exact same issue as you (doze worked for a day or two, then seemed to have a bug with WiFi), and after several days of troubleshooting I finally went into WiFi settings --> Advanced --> Keep WiFi On During Sleep -->
Only When Plugged In
That fixed it for me. I believe there is a bug keeping WiFi on during Doze, even though WiFi is supposed to be 'sleeping' during doze. To support this theory, my battery graphs always showed WiFi on even when I manually disabled WiFi altogether, dozing or not. This won't affect anything, because Doze is supposed to mostly turn off your WiFi anyway. Now I lose between 0% and 2% overnight. For example last night I went to bed at 10PM with 41%, woke up this morning at 7:30 AM (9.5 hours later) and it was still at 41%. Amazing. I literally get 3-day battery life thanks to Doze. I'm currently 60.5 hours since my last charge and I have 37% battery left.
I also turned off the "follow me" feature in location settings, and my location settings are set to "battery saving" (No need for high accuracy unless using navigation). Not sure if those made a difference.
I also find that using DND mode of any kind while sleeping makes my phone use 2-3% overnight compared to 0-1% without. Not a big deal, but I do believe there is a tiny difference. You can also just make your ringer/notification volume low and alarm volume high for the same effect.
Lastly, regarding WhatsApp, unless the app is fully closed, and not running in the background, it eats battery. It did on my N5 and it does on my 6P. Nothing major, but it's noticeable.