When using Android Studio to package up an Android Wear app into a signed APK a missing manifest permission in the phone app can break the Wear app installation.
There are no errors in the gradle build or when creating the APK. You can try to install the APK and it will succeed on the phone, but the corresponding Wear app won’t install on the watch. There will be no visible errors on the watch or phone to alert you to this.
If you are debugging your application then there are errors reported in the logging but they can be very hard to spot because of the constant flow of debug coming from the watch.
The solution turned out to be that you must replicate any android permissions that the Wear app needs in the phone app’s manifest file.