1. 确认是否为客户端问题：可以使用其他websocket客户端测试是否出现同样的问题，如果是，则继续下一步；如果不是，则需要检查客户端代码。
2. 确认后端代码：检查后端使用的websocket库是否正确配置并支持多个会话。可以考虑使用actix-web的其他websocket库，如tokio-tungstenite。
3. 代码示例：

use actix::*;
use actix_web::*;
use actix_web_actors::ws;
use std::collections::HashSet;

struct Lobby {
    sessions: HashSet>,
}

impl Default for Lobby {
    fn default() -> Self {
        Lobby { sessions: HashSet::new() }
    }
}

impl Actor for Lobby {
    type Context = Context;
}

impl Handler for Lobby {
    type Result = ();

    fn handle(&mut self, msg: Connect, ctx: &mut Self::Context) {
        let my_websocket = MyWebSocket::default().start(ctx);

        self.sessions.insert(my_websocket);

        msg.addr.do_send(Connected(my_websocket));
    }
}

struct MyWebSocket;

impl Default for MyWebSocket {
    fn default() -> Self {
        MyWebSocket
    }
}

impl Actor for MyWebSocket {
    type Context = ws::WebsocketContext;

    fn started(&mut self, ctx: &mut Self::Context) {
        ctx.add_stream(stream::once(Ok(ws::Message::Text(
            "You are connected".to_string(),
        ))));
    }
}

impl StreamHandler> for MyWebSocket {
    fn handle(&mut self, _msg: Result, _: &mut Self::Context) {

    }
}

struct Connect {
    addr: Recipient,
}

struct Connected(Addr);

async fn index(req: HttpRequest, stream: web::Payload, srv: web::Data>) -> Result {
    let resp = ws::start(MyWebSocket {}, &req, stream, |out| Connect { addr: out });

    resp.map(|req| req.on_upgrade(|ws_conn| handle_websocket_connection(ws_conn, srv.get_ref()).map_err(|_| ())))
}

async fn handle_websocket_connection(ws_conn: ws::WebsocketContext, lobby_addr: &Addr) -> Result<(), ws::ProtocolError> {
    lobby_addr.do_send(Connect { addr: ws_conn.address() });

    Ok(())
}