The "Live preview feature" has stopped working and so did the "Nickname auto-completion" thing too, anyone knows why?_?

The “Live message preview” feature used to be working perfectly with me yesterday, but today, it just never appears at all!

And also, the “Nickname auto-completion” thing that pops up when you type the ”@” character with a certain letter next it, it used work with me but now it just never works, what’s wrong?