Full screen

While reading posts/comments from 2–4 days ago, I noticed something. When people go fullscreen, their videos fill the screen, but mine has black bars on both sides. Is it my phone settings or something? I watched on TV and computer, and it fills the screen there with no black space. I also remember when I first watched on this app, it used to fill the screen or go fullscreen without the black bars. Or maybe I’m just imagining things.

Anyone else having this problem too, or just me?