You can try add these to your nginx conf inside location / { like this:

proxy_set_header Connection "keep-alive, Upgrade";
proxy_set_header Upgrade websocket;

like this:

location / {
         .... 
         proxy_set_header Connection "keep-alive, Upgrade";
         proxy_set_header Upgrade websocket;

}

I launched my instance last weekend and this was my issue as too.