Same issue. I just got a new Air to replace my ageing laptop and hoped the issues would be gone, but nope, exactly the same problems. Xcode randomly decides that my watch is not available for development. With some luck it starts working again, but then I usually get the running but not really running problem instead. This time it was magically fixed by restarting Xcode after which it finally installed the app and managed to start it. What can possibly be so different with our setups compared to the Apple developers? I can't imagine they would put up with this every day.