Starting with the rollout of Hangout as an update for gtalk (both inside gmail and as the android client) that happened around May, I noticed that I kept missing some messages and realizing someone tried to contact me only several days later.The way I look for missed old messages is with the label:chats of gmail.Please note that I don't actually use Hangout (due to its well-known shortcomings): I reverted the gmail interface to the old one and disabled hangout notifications on android... instead I try to use XMPP clients as much as possible.The last time that this happened was this morning: a friend wrote me before I connected my phone and I powered-up my tablet and pc (the pc was in standby with a browser tab containing gmail), so there was nothing connected that could've triggered Google to think: I won't bother notifying the user for this message, since he already received it on a connected deviceBefore the Hangouts app rollout, I saw the messages I missed when openining up gmail: they'd be open in the bottom right of the window and I'd often see them shown among the mails as well. Now there's no clue that someone tried to message me.PS: I realized that the problem is indeed that I never appeared as offline to my contacts... I'm always at least away, but never offline.I forced a sign out from other sessions in gmail, but this didn't affect anythingI tried to create another gtalk account, to chat with myself and debug the problem: this way I noticed that when I should be offline, I have 2 XMPP resources from which I'm connected.Unfortunately, unlike gmail, ChatSecure and jitsi, who publish the application name in the resource name, these two follow the pattern MessagingAxxxxxxxx (the x are hex characters). So I have no clue what could've possibly generated these resource names.At last, I activated 2 factor authentication... this disconnected every account that I had connected, except for these 2 phantom resources. I think that this is, as baffling as it is, proof that the problem is on Google's side, on their servers.
Gtalk unnotified messages
gmail;notifications;google talk
I found out the problem: I realized that the Messaging resource was being used by every gtalk contact, except those who weren't connecting through the google server.Also: some people had a double Messaging resource just like me... Maybe the culprit was the android Hangout application?I disabled the notifications inside the app: the user expectation is that it doesn't get any push notification from the server nor notifies the user through the android notification bar.Instead, what is actually implemented is only the latter part... worse: even if the device has been powered off by several days, the application asks google's servers to keep a phantom resource connected.This is the crux of the issue: apparently the option for disabling notifications on the android app is completely broken and useless, with this behavior.The alternatives would be to uninstall the app (if at all possible... but this would lose the Video Hangouts capability) or just remember to manually sign out (you have to open the settings to do it!) each time you open the app, even if by mistake.