I just got a new MacBook 2016 with Mac OS Sierra installed, after setting up my complete development environment and all required tools via Android Studio, I tried to flash a new Android Wear release on my watch.
ADB is working without issues, but as soon as I try to run any fastboot command (other than fastboot help) it will completely freeze and never finish.
It is just stuck with no output at all.
I already tried to run it with sudo or reinstall it via the SDK Manager, I also tried different standalone fastboot binaries provided on XDA developers.
There is nothing which seems to make it finish. Even "ctrl + c" won't exit the running command. Only killing it via the process list will work.