Ok - at present the underlying websockets library will attempt to connect using websockets first, and failing that, drops down to ajax polling. This is why it takes a couple seconds.
As long as you eventually get connected, it's okay, although we do realise that it is a problem for some people.
Seems to happen more often after a restart, after the first 404s it will eventually start pulling posts properly then at some point the connection will go stale and it'll 404 again. It's pretty consistent for me. About to try it out on the latest pull. Nothing in the logs/dev mode. Just 404s in the console.
I just realize that there is already that problem and it was resolved (by wrong search). So, when i did the update, I updated nginx too. So here the post :
So it solved.