I don't know whether I found a solution, but I resolved the problem for my case. Normally I would have XCode saying: "Running .. on .. Apple Watch", then it would sometimes say " Unable to install ..". However, after I removed "Connect via Network" in Window -> Devices and Simulators -> Paired Device the error stopped.

Have you found any solution to this problem?

Did you find any solutions?

The watch app extension was registered with my free plan account under the same identifier and caused the conflict. Apple had to delete that identifier in order for it to be assigned to my 'real' developer account.Somehow I managed to register my watch app extension with the same initial bundle identifier as my parent app. However, rather than registering it with my real developer account I did so with my free plan account, hence the "Failed to register bundle identifier." error.Surprisingly my watch app (not the extension) was registered under my real account which bugs me, since they are both created at the same time when you create the watchOS target.The problem with that is, that as a free user you cannot look into the identifier registered under your account. You have to ask Apple to delete the identifiers for you. After that Xcode was creating a new provisioning profile.