Windows, by default, doesn't fully power off when you tell it to shut down. Windows Update can wake it up and install updates, and then leave the computer running when it's done.
I believe there are some registry and/or group policy settings to disable this feature, but I'm not sure specifically what they are.
An option in the meantime is to hold down the left shift key while as you tell Windows to shut down. This should force a full power-off.
Some more ideas:
Possibly doing updates? I know something along the lines of "use my credentials to finish updating after reboot" is an option, but I was pretty sure that just got past the "We're getting you PC ready for you" screen & dropped you back to the login screen
I don’t know about the auto login, but a couple things I do is:
I had a similar problem. Tried a bunch of resolutions, fixes, or configs and none of them worked. Just bothered by it one day where I had just put the box to sleep and I just barely nudged my desk, wireless mouse lights up because it detected movement, box wakes up. My overly sensitive mouse was picking up shaking and waking up the computer because of the mouse input.
I figured that was the case so I turned my mouse off and unplugged my keyboard because cat and it still happened.
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?
It isn't a huge issue but I just wanted make sure it wasn't some weird virus or something that snuck its way in on a mod or something
Is there any risk to messing with the powercfg?
Unlikely a virus, but not impossible. Just more likely to be microsoft up to their normal tricks.
You can certainly make trouble with powercfg, but doing 'powercfg /lastwake' is entirely informational.
Wake on LAN. You can turn this off in the power options I think, or in the BIOS.
As for automatic login, that I cannot say. Maybe you activated the option somewhere?
Whenever I wake it normally, it always opens to password input but every now and then I pass by the room and notice it's lights are on when I know for sure I put it to sleep and sometimes when I wiggle the mouse to take it off screen saver, it's logged in. Never really messed with any settings in that respect but I'll dig deeper there
Maybe someone is doing remote desktop on you.
That's essentially what I'm trying to figure oout. I've never done any sort of screen share and I run a pretty clean machine unless something snuck in on a game mod I downloaded
Suggest after use disconnect it from the network. Observe if it still wakes up and logged in. If it does not then you can assume that your system is compromise.
There is also this. https://superuser.com/a/1250547, but since you mentioned that it is intermittent then I doubt it might be this.
Another action you could do is change the password of your account. See if it still logged in.
Time to run an offline malware detection tool. Something you can boot into using a USB stick or something.
Yeah I would be a bit worried about that...