I get the first message, and any others in the same conversation soon after don't vibrate. I've responded late because of this. Its annoying. Help?

I'm using hangouts by the way.

Edit: I've tested this, and it only seems to happen when I get a message, and reply. After that, it won't vibrate. When I turn the watch on it shows I have a text message, and when I pull it up to see it, it shows the previous message, then vibrates and shows the newest one I just got.