Yes, I understand - I suppose the emergency power could be running but the avionics are dead with gens not on but trust me - this is a bug - the backup attitude indicator is dead too… has happened to me and I did over a dozen flights trying to find settings to keep it from happening with no luck…
I’ve had it happen on taxi, takeoff roll, cruise, tod, approach, and short final - triple checking the overhead and making sure there was no issues with panel brightness.