I have an app based on Google Cloud Messaging and it was working well. Now (today) all of a sudden it started having a problem we've never seen before. For each message sent between devices, the receiving device will get it twice. The first will arrive almost instantly (within less than 3 seconds of sending). The second arrives a few minutes later. There are two devices in the test, the problem is the same whichever one is the sender/receiver. So if a device sends a few message to the other, the other will get them pretty much instantly--but then at a later time, it will receive a barrage of messages which are the second copies of the messages it has received.
I have put in breakpoints to make sure that the sending device wasn't the culprit: the message was sent exactly once (i.e. the web service for sending was called exactly once--and the code for the backend, which runs on Google App Engine, hasn't changed for ages.) However, the message somehow gets delivered to the receiving device twice. By using breakpoints I also made sure our own code on receiving side isn't responsible: it is verified that GCMIntentService::onMessage() indeed gets invoked twice for each sent message.
We also made sure the registration id in our database is the latest. At this point I'm stumped and need ideas to make any further progress. So any ideas?
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