Greetings from the third world country that is Scotland. A land in which it’s seemingly impossible for power companies to maintain an adequate supply for longer than a couple of months before a power cut strikes.
I can tell when I’ve suffered another of these when the microwave’s clock shows: 00:00. My Mac and Linux computers were also powered off. Luckily they have journaled file systems, so no data loss has been detected.
I run High Sierra, 10.13.5, so I used System Information (alt About this Mac) to examine the Power Management log, under Software/Logs. This showed Scottish Power(cut) had failed to provide enough juice at or shortly after 02:35:14 am. Below that you can see the power off and reboot times.
2018-07-07 02:35:14 +0100 Assertions PID 39(UserEventAgent) Released BackgroundTask “com.apple.backupd-auto” [System: BGTask]
Time stamp Domain Message Duration Delay
========== ====== ======= ======== =====
2018-07-07 10:25:13 +0100 Start powerd process is started
Call me a cynic but that timing, looks suspiciously like a planned reboot.
Regardless, Scottish Power(cut) are a shower of bastards and renationalisation is the only answer.