Following up the first part of my story. After finding another Octatrack, second hand but still under warranty, my first Octatrack is on its way to repair.
Today, same story. A show in open air, hot afternoon but not excessive (weather service says 28°C), after about one hour of service this other Octatrack crashes the same way : screen goes blank, sound shuts down, LEDs stay dim orange. I have to power off and on to restore service. Following that first crash, other ones happen every now and then (5 to 20 minutes).
Other gear on the same table perfectly stay in service.
That second machine seems to be manufactured around the same time as my first one.
Needless to say, I am not happy.