Apple launched watchOS 5.1 earlier today, but has temporarily removed it from accessibility after users reported that their watches were rendered useless by trying to install the update. 9to5Mac s Guilherme Rambo experienced the problem, as well as more MacRumors readers.
Serious issues with Apple Watch can be more complicated to resolve than with iPhones or other devices because it is not possible to connect the device to a computer and reinstall the software yourself. The only measure tends to be to contact Apple for service. The problem seems to be limited to the brand new Apple Watch Series 4, which is also likely for complex frustration for affected users.