This happens for me as well, I usually have to quit out and then rejoin or just join a different server.

The animation should not be so sluggish, and the hit should not be so precise. Melee weapons should be like shotguns and have some leeway as to having to hit directly onto the zombie at exactly the right time. You should also be able to swing faster.

Usually the bodies glide across the ground for a little and then just completely disappear, this happens for my friend and myself.