When I try to @ a user in the app, it does not give me auto-fill suggestions for tagging, even when I spell out the name completely. 

If we can't @ in comments, it's really hard to give heads up and get chatter going on a post. It's really vital to keep momentum. When it glitched on the desktop, our kids felt really out of touch from each other. This is a basic feature in all social networking apps and hope we can have it here