Sometimes when I use 9gag only the photos, gifs and videos flinch when I don't watching them, rest of the apk works like it should. I don't know if it's the phone or the apk.
Perhaps try uninstalling and reinstalling the app? If that doesn't resolve it, can you post a video? I'm not sure I know what you mean when you say flinch.
Perhaps that is a stutter that is Wi-Fi connection or network related.
It's just photos but sometimes it happens sometimes not.
Weird. What happens if you use a different browser? Would this happen in Chrome?
On a similar service, like reddit, does scrolling through images like that lead to flickering?
I think it's just the app, but I think it can be the app and not the phone that make the problem but have never notist that on any other device.
In that case, we can safely consider this an app issue. If you notice it happening with different apps, then we can investigate in more detail.