So I've just attempted to recreate your issue and ran through the sample with the latest version of Cordova (6.3.1). I'm also running the newest version of Android Studio:
There was some lag when initially sending my Push notifications (it probably took ~5-10 minutes after initial registration for me before they all started to come through).
Before sending:
After sent:
From your issues, on the top of my head, I think of a few things that could have potentially gone wrong:
There was some network latency after registration, and the Push Notifications would have eventually come through.
Your GCM / Push Notifications service was configured incorrectly. To test this, I would try out the Android hellopush sample to see if I can get anything.
Different versions of Cordova or the emulator could be the culprit.
It could be something else entirely :0)
If you keep running into issues or #4 is the case, I recommend opening up a support ticket with your Push Notifications service instance. This should provide a little more of your app information to the Bluemix Mobile service team, and they should be able to look at the server logs to see what is happening to your notifications.