Planes like the 787 are probably very rarely completely powered down. At the gate, they're on ground power and there are probably some power buses left energize

Planes like the 787 are probably very rarely completely powered down. At the gate, they're on ground power and there are probably some power buses left energized even if the plane is going to sit unused until the next day. These generator control units (since the article says they take an hour to boot up...running through a ton of tests, I guess?) are probably energized even when most other aircraft systems are turned off. If the aircraft is being towed to a hangar or away from a gate for parking, they probably want its lights on while in motion on the field so will stay powered from battery or fire up the APU (auxiliary power unit) before disconnecting from ground power to tow it around. When it makes it to the hangar, perhaps it gets plugged back in to ground power. So it's conceivable that this particular component could remain powered up continuously for a looong time. That said: as others have stated, some forms of maintenance would power down the plane completely, and these likely happen more often than this overflow bug occurs. If I remember from the articles when this bug was first discovered, it was discovered through simulation or specific testing and not because an operator encountered it, which would imply that yes, operators do "reboot" the whole airplane often enough where this doesn't naturally happen.