Windows 10: PC is still rebooting from hibernate :(

Still no dice. I will smash this thing into fancy silicon bits. Nah just kidding; I can leave it running if needed.
I put it on hibernate after staying up past bedtime and it's booting again with Unknown Source. I'm gonna do a full shutdown again, then try hibernating with no running apps (aside from startup apps). Maybe even try disabling services and startups, but I'll leave that up to if someone says to.

 

More specifically, it had rebooted immediately when I hibernated, rather than pausing a minute or anything.
After a full shutdown and hibernating from a fresh boot, the PC was off all night, however it required toggling the power switch off and on in the back this morning before the power button would function. This isn't the first time. Often when I had this hibernation problem, I'd push the power button quickly after the PC booted itself, and the power button later required toggling that switch for a few seconds.

 

As a test, how does it perform when you have Fast Startup turned on, and shut down instead for a hybrid boot?

 

Ok, so, possibly unrelated, but I might post in this thread again in case it is...
My PC shuts itself down and reboots, but hangs on some MBR error, which I ended up eventually finding that I don't have to fix my installation, but rather change my boot menu. But the boot menu doesn't stick, which suggests needing a new CR2032 battery or whatever for the mobo. I haven't gotten around to trying that.
My GA-970A-UD3P rev1 mobo BIOS doesn't play nicely with my Korean QNix-brand 2560x1440 monitor, so I sometimes have to hunt down another monitor and fuss with cords behind my desk to force it to boot my SSD.
But PowerTroubleshooter doesn't seem to show what shutdown my PC. I don't know where to find what causes a reboot in the first place.
See, as you likely know, the other problem was me triggering hibernate and random booting back up, but now it's just plain rebooting. Windows Update is set to notify to schedule restart and I've seen no notification. I just need to find and disable whatever's rebooting me, especially when my boot order isn't sticking (I'll get a battery... eventually and see if that works).

 

I look forward to your findings.