Hi, this happened to me many times... maybe 5 times:
During the flight helicopter systems shutdown randomly for a while. HUD, gyros, ADI, generators, transformers, rectifiers, autopilot, hydraulics, engine gauges were down. After cca 15 seconds systems go up again by itself.
I was not pressing any buttons or switches in the cockpit at that time.
It happened to me during flight after cold and dark start and also after start in the air.
issue.trk