Genexus X Evolution 3 - Device registration for notifications does not work

I have an online application for Smart Devices created in Genexus X Evolution 3 (U2) wich has notifications enabled (only for android at the moment) but for some reason that I don't know, I can't register the devices to send the notifications later. This are the steps that I followed:

• I have created the credentials (API Sender ID & API Sender Key) For the Google Messaging Cloud Service just like the Wiki said.
• I set up my Main Object (SD Panel for Smart Devices, NOT Dashboard) with those credentials.
• In this same Main Object I use the procedure NotificationRegistrationHandler in order to automatically register the devices.
• I created a transaction (named "Device") with 4 attributes (The ones that are "in" parameters in the procedure NotificationRegistrationHandler)
• Then I un-comment the code in the procedure. It matches my new transaction, navigation is perfect.

In theory, this procedure should be excecuted automatically everytime I launch my application and register the device in order to be able to send it notifications later. But the registration never happens. I have though a blank notification at launch and I don't know why. (Here's an image: https://i.sstatic.net/Inqqe.png).

Why could this be happening? Is there something I'm missing?

Best Regards.

Upgrade 3 for Xev3 includes a fix for this empty notification. Look at SAC #37858