Attack animations not synced + some rendering bugs

[rickguedes]

Hi,
I have deployed a server as-is from this repository and noticed some bugs that are not present in the original mozilla version. You can't see other players attack animation anymore (they just stand still and the mob dies randomly). You can see yours correctly though.
Also, sometimes the players just turn invisible when it's supposed to render some effect on them. (You can check this by mousing over other players, and also when taking damage. You will blink for a second)

Any ideas about what could be causing them? I checked the commits but couldn't find anything obviously related.