I have upgraded my bios from 25.1 to 25.3, issue remains. I will browse the
BIOS for overclocking settings, but I didn't change any; so if they do effect
this, then it's the factory-defaults causing this.

This is a wild guess, but the symptoms to me look like a spurious watchdog
kicking in, given that the system appears fully functional right up until the
reboot, no errors are logged and there is a delay between the modprobe and the
reboot.

@Kertesz: according to Alex in comment #1, "forcing dpm=1 will enable extra
debugging output". Possibly that's why you're not seeing those lines.