Race conditions in client synchronization

I have a web app whose server creates a Client for each websocket connection. A Client acts as an intermediary between the websocket connection and a single instance of a Hub. The Hub maintains a set of registered clients and broadcasts messages to the clients. This works pretty well but the problem is that a client might miss events between when the server generates the initial state bundle that the client receives on connection and when the client is registered with the hub and starts receiving broadcast events.

My idea is to register the client with the hub before any information is fetched from the db. That would ensure that the client doesn't miss any broadcasts, though now it could receive messages that are already applied to the initial state it receives. To allow the client to disregard these messages I could include a monotonic timestamp in both the initial state bundle as well as broadcast events.

Can you think of a more elegant/simpler solution?