So I think I finally found one of the problems with figwheel websocket connection. Apparently doing a websocket/send inside the websocket/on-open callback was causing some problems. I've looked around for documentation on this but really couldn't seem to find it. The clue was that the internal architecture is completely async now. So my assumption now, is that I'm sending a message to the client before the client is actually ready to receive it. So it ends up in a race and blocks. This was a problem before but got much much worse under the new Jetty Server. Anyway I've updated the 0.2.21-SNAPSHOT hoping that this solves some of the initial connection problems that have hindered figwheel startup for a while.