Push notifications have stopped working for me. I have tried sending notifications through the Appcelerator dashboard but the request fails with the log GCM Error 3009 (see image attached below). My GCM configuration with Appcelerator's Arrow Cloud Service has not changed and has worked previously. I did update my project from 5.3 to 5.5.1 but going back to the previous version didn't fix the issue.
On the app side, I confirm that I am successfully getting a push notification token, logging into ACS, and subscribing to a channel.
Because Arrow Cloud Service is our server in relations to GCM, I'm not sure what I can do. 
What worked for me was:
1) log the device token of the device not receiving the push,
2) in the appc dashboard, go to the Devices tab and unsubscribe the android device with the matching token.
3) re-launch the app, make sure you're subscribed successfully, and the device should now receive push notifications.