I do not have detailed info on how it works, but I know for Android the device gets unregistered if you send a message to an invalid registration ID. The push notification module takes care of this by handling the reponse payload.
The registration ID is fetched every time you start the app. You should check the device registration ID in the database right after you started the app, and take it from there. Let us know if you need more info.
Push implementations for iOS and Android are a bit different.
Generally, at a very first time to launch your app, it tries to register the phone's ID to Mendix Server as well as Apple or Google server.
Maybe, your ID disappeared in Mendix Server. Your ID is automatically cleaned up at Apple or Google server.
The solution is simple. Restart your app.
If it does not work, that's PhoneGap or Mendix bug!
@ Wilfried and @Isamu
I actually have a problem with the registration of my Android device. I did follow the same instructions as above, but I my device does not get registered.
Does anyone know what could be the problem?