[nearlysober80]

I've been using the Hangouts app for both hangouts & SMS for a long time. I've also had my Gmail app configured for a long time, never had any problems. Awhile back, my AT&T Galaxy S4 upgraded to Lollipop. Recently, I've noticed unreliable behavior from both applications when I have incoming messages. I have no changed any application level settings.

Hangouts Behavior:
Without any notification of new messages, I'll open up Hangouts and either on the list page, or when I go into a conversation, I'll be notified that I have unread messages. Sometimes they'll be hours old, they are marked with the appropriate time stamp. At one point I was sending a text in one thread and after sending, was notified I had received a text hours earlier on.

It's acting pretty odd... right now it shows a group SMS conversation down in August 2014, despite me getting updates on that conversation yesterday (the conversation still has yesterdays messages in it).

Gmail Behavior:
For Gmail, the app just seems very slow to update me of notifications. I'll show no new message, no notifications and I'll open the app up, then it'll show an email from several hours earlier.

What I've tried:
Cannot uninstall either app, so I reverted back to factory settings and re-installed updates. This seems to have caused my recent SMS conversation to go back several months despite being active yesterday. Checked all my notification settings from applications & phone itself, nothing seems odd. Tried rebooting phone of course. Cleared app data, cleared app cache...

More info:
Samsung Galaxy S4
AT&T (issue seems the same on network or WiFi)
Lollipop 5.0.1

[jetspeedz]

having the same issue on gmail and new s6, I've used a combination of Gmail app and OS email app both do the same, it leads me to believe it is a network/server related issue and nothing to do with the phone. Quite irritating coming from push email on blackberry.

[Peter Steier]

Quite annoying; waited for an important e-mail to start to do some work on it, and got no notification till 14:30. When I looked into gmail manually, it was not htere yet. I deleted all old e-mails, and when I wanted to quit gmail, suddenliy the mail arrived - with send date 09:15. I have lost a complete work day, will cost a few hundred €, because a big scientific instrument was not used efficiently. Fortunately, I work for a government, so it is tax money ;-)
These gadgets are just toys.

[jetspeedz]

You need to contact your carrier and Samsung if you want them to fix this quickly. I have made countless calls to both and they both had no idea the problem existed until i reported it but now they agree there is a problem. However, how quickly they fix it depends on how many people complain which is sad but that is how it works.

[katana-d40]

I had the same problem with my Xperia after a Cyanogen update to 5.0.
It only happened when using cellular data. The problem was the authentication method of the carrier.

I opened the APN and selected "CHAP" authentication, that fixed the problem,