Hi MC,
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...
Other possibility:
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.