My first educated guess is that you running the application behind proxy http server / load balancer, and have not configured it to route also the websocket traffic to the application server and using @Push(transport = Transport.WebSocket). There are couple of alternatives for you. Easy one is to change to @Push(transport = Transport.WebSocket_XHR). With this option the traffic from browser to server will be http and traffic from server to browser WebSocket. So then you do not setup your proxy to support WebSocket traffic. Another alternative is that you configure the proxy.
Tomcat is responding directly without balancer or proxy
I will test with @Push(transport = Transport.WebSocket_XHR)
If the problem persists, I will try to place a proxy.