Identity mod not working correctly

I created a mutliplayer Aternos server with the Identity mod and its dependency (Architectury API), and everything was working fine until my friend joined the server. He was able to transform into mobs, but I couldn't see his transformation. For example, if he turned into a ghast, to me he would still seem like a regular player. In addition, whenever we would be our regular selves, an item that we're holding would appear in the middle of our bodies instead of in our hands where it's supposed to be. Does anyone know the solution to this?