Maybe there is really something behind this - but I'm also not sure.
But, once in a while (at least I experience it that way) my ADI-2 Pro also turns automatically on when I switch on my "Steckdosenleiste". This happens once in two months or so. And each time I was very (or should I say "quite") sure that I turned it off via the Power-Button before because in general I never intentionally cut power when devices are turned on.
And, this is independent from the firmware - the behaviour was right from the start "observable" (I bought my device in May 2017).
So, this could be indeed a very rare condition with the ADI-2 Pro (which I now believe in even more). Otherwise I would call it my own "brain" bug...
Someone else has turned the device on and disconnected power without switching off. In my situation this is quite unlikely but could be relevant for others.