Hostile mobs are not showing

I have a zombie spawner near my house. If a lot of the zombies spawn near each other, sometimes it will happen, that 1 or 2 zombies appear invisible, and hit you. You can't even try to hit them, it's like nothing is there.

It also happens when I'm under the ground. I have a large area digged out under the Ground, and a lot of slimes also spawns. It happened there too.

It's just a annoying way of dying, I hope this will get fixed!