it happened twice in the past 6 days, as far as i'm aware of.
just upgraded to 18.06.1 today as soon as i found out.
i was thinking of a way to keep track of such reboots so.. i figured out
date >> path/to/somefile
would do the job, so to keep an eye on it for a while, just in case.
Firstly my intention was to bring the case to your attention and
secondly to ask if someone has any wiser ideas on how to keep track of and realise future incidents.