Well, this is embarrassing. Yesterday Apple released watchOS 3.1.1 to squish various bugs. Now, as noted by MacRumors, the update has been pulled because it’s bricking some Apple Watches.
Affected Apple Watches are displaying a red exclamation mark on the screen that instructs them to visit www.apple.com/help/watch. The site directs Apple Watch owners to perform a force restart of the Apple Watch by holding down the side button and the Digital Crown, and says that if a restart does not work to restore the device, it will need to be taken in for service.