Reminds me of a good excuse I heard although, at the time, I did not know it was an excuse.
HKG January 1995 (Kai Tak
) Sitting on a VS A340 (a -300 I think but someone will know) and the flight was full as it was last out before Lunar New Year. Waiting around and flight deck warned of having to power down to reset the entertainment system. "We don't want you to not have your films and music during the long flight" It was extra long at 15.25 hours as we had to divert north almost to Beijing, to get around a cyclone, before turning West.
A couple of years later I learnt of the early computer sync problems on the 340. If, on start up, the 5 computers could not agree that they were all in the same place and on the same line of code - you had no choice but to power down the WHOLE aircraft. A classic, "You have to switch it off, wait a couple of minutes and then on again"
It worked and it was prob best that 99.9% of the pax did not know that there was nothing wrong with the IFE ...