Sovereign Check your Client_Prev.log. You can sometimes see Failed to find player: xx. That means your client sometimes doesn't get the information that a new player connected to the server, this will result in [?] when you die from that player. And of course you can't hear or see him when your client doesn't get the info to add him to the game. [?] isn't always the same player.
The thing is, if you rejoin, your client will ask for all players again. ⇒ [?] is gone.
But that's just a theory.