Ahhhh that'll explain never receiving messages and my friends not getting them. Some bust scenarios I experience:
1. I will call my wife using Hangouts - she won't be notified on her phone.
2. I chat with someone via Google Talk on my old phone - if they're using Hangouts, they may or may not receive the message.
3. Someone will chat with me via Hangouts. My phone with Google Talk may or may not receive it; BUT! if I open the web browser version on a laptop, it'll receive it (and makes me look like an ignorant weirdo when I reply to messages that have been "there" for days...
Mobile hangouts to mobile hangouts mostly works (apart from the video call at intermittent times). Oddly, the Hangouts client will say that the person was not available for a video call (ie, they didn't pick up) but they didn't receive any alert or ANYTHING to state that there was a call coming in.
No offence to the team there, but it's a piece of junk. Video calling and voice calling and text all worked fine under Google Talk; under Hangouts, I might as well be putting messages in bottles and hoping they will reach the destination...
Even MSN Messenger was more reliable, and that was 15+ years ago; I am not sure how this is not a solved problem! (Not sure if they've fixed the lack of online/offline presence in Hangouts yet; if not, it is STUPID. "Are you there?" Who knows!)