Once or twice a year, even in the Windows Home Server 2011 days, I'd get a nasty, scary backup database warning. No idea why it happens, but I do have about a dozen machines backing up daily, some at home, some remotely via VPN. That's roughly 3TB of space needed for just my Client Computer Backups folder. Yes, that's a lot of HD videos.
This video will show you how simple it is to repair the database when trouble occasionally strikes. I should also point out that such a repair tend to take hours. So it's pretty crummy when it happens, especially if you were about to try to restore a laptop backup, since you won't be able to do backups or restores during the repair process. A warning message will stop you in your tracks, when you attempt to perform such activities.
Good news is in the short video below, where you'll see just how easy it is to resolve this issue, and a closer look at what processes run when it churns away for hours. In my experience with such incidents, most of the time there's no backups lost whatsoever, which is even better news!