The mixers are doing an "auto save" every 30 or 40 seconds. If a power failure catches the board right in the middle of an auto save, there is no "previous state" any more and it looks like that the boards then tend to revert to default. This was reported and discussed in the forums (search for UPS or power failure). There is not really anything you can do against it, especially if the boards are running 24/7, as I guess from what you write. You have do everything (!!!!!) to prevent any power failure, power drop or power peak. Digital concoles are computers and therefore not very "resistant" against power problems!