React doesn't accept event stream from flask

Question

So I'm trying to send data from flask to react on every hour for example, since this is a server push thing I decided to go with Event stream push from backend. Server is pushing as it should, but on React side I always get an error

This is backend code:

@app.route("/stream/<int:uid>", methods=["POST", "GET"])
def stream(uid):
    # if not uid:
        # # todo not implemented
        # # 503 - Service Unavailable - server is not ready to handle the req
        # return {"msg": "UID not provided"}, 503
    def eventStream():
        print(f"connected uid: {uid}")
        while True:
            if config.updated_flag == 1:
                data = Investment.get_all_by_user_id(uid)
                print(f"yielding new data now | time: {datetime.now()}")
                config.updated_flag = 0
                yield f"data: {data}\n\n"
    return Response(eventStream(), mimetype='application/event-stream')

This is the frontend where I'm accepting the eventStream:

useEffect(() => {
      const sse = new EventSource(`${serverBaseURL}/stream/${props.userId}`, );
      sse.onmessage = e => {
        console.log(e.data)
      }
      sse.onerror = (err) => {
        // error log here 
        console.log("error"); 
        console.log(err)
        sse.close();
      }

      return () => {
        sse.close();
      };

    }, []);

On the first push that server does, this is the error that I get:

After this error, server is still yielding data, but there is nothing happening on the client