I was having that issue on my LGG3, but I've had the s6 for a week now without that happening (fingers crossed!). I found that restarting my phone helped, but that's pretty impractical. I'm still having trouble in that it's taking awhile for a hangout to get to me, even though I know it's been sent (I can see the sender typing). I'm taking life at least 10 minutes or so.