When player hits another player that's blocking the shield goes down visually

So when I'm on my any server, whenever a person is blocking their shield and I try to hit them with a sword or a bow. There shield goes down visually, even though they're still actually blocking on there screen. As well when I hit them they don't take any damage like the shield would normally do.

Footage: https://www.youtube.com/watch?v=t4lx5SH_GdI

Note: Forgot to show it in the clip but It's not because of my resource pack, It has happened without it as well.