There’s always desync in multiplayer. Even on LAN there’s ping variance, then game and render thread variance. Rep_notify variable won’t mitigate desync.
Op is trying to execute logic when the player has loaded. Special event. In order for the server to know when a client has loaded you need the client to tell the server it’s ready.
Ops other constraint is one and done. One RPC call to handle all clients. Thus multicast.
Rep_notify requires the creation of a variable and a function that will persist. Thus is bloat. A dispatcher call to the server is a one and done per client. You can even unbind it when done. Once all are ready the server can fire a single event that executes logic on every client. No loops, no passing variables etc. The packet will have a simple event call in it.