https://superuser.com/questions/955262/pc-waking-from-sleep-for-unknown-reason
It is windows, so your deep debug/fix options are limited. I've had some luck with the 'powercfg' commands disabling sleep/wake for some sources.
The other suggestion, wake timers, is probably your problem, since windows wants to stay out of your way, and in their mind that means to wake up at 3am to take updates.. what could go wrong?