Because the server is firing an event before the pawn exists on the client. That’s the whole point of the client notifying the server that it is ready. Not all load in fast. Varying hardware/software, background services, apps etc.
Look at Battlefield for example. Pre-round all clients have to ready up before the game start countdown starts ticking. Thus each client has to call the server to notify it. When all have readied up, the server fires back an event to start the countdown.