At that level it is usually the console rebooting. On a large show even 15 seconds can seem like 5 minutes. So it becomes important how long it takes for the mixer to reboot and how soon can it pass and process audio. There are some well known and widely used digital mixers that start passing audio before you can actually use the faders or mutes. This can have really bad consequences too. 90% of these things happen due to power issues. So a lot of companies now use UPS on the console so that it will stay running even if the power drops momentarily.