Now it's gone again, and the total number of Early-bird devices remains at 1192, as before, so, I suppose, either someone requested a refund or it was some kind of fluke.
Edit: As I seem to still keep an eye on the Indiegogo Cosmo page; today on December 13, about a week after the crowdfunding ended, a single early-bird unit was, again, briefly available for $549. As I know from the Indiegogo comments, that a few backers indeed has changed their minds and requested refunds, I feel quite confident that these briefly appearing units are indeed devices for which their original backers have asked for their money back.
Perhaps that's just how Indiegogo works, or perhaps Planet Computers feels it's easier that a device for which they have accounted, say $549, remains at $549. In either case, that could mean we'll see single week3-specials units reappear at $569 too.