If it's a self signed certificate you didn't accept manually before then yes, it's normal. The browser will refuse to connect since it doesn't trust the certificate. Try opening the HTTPS version of the websocket address in a tab, accept the self signed certificate, and then it should work. Of course that's only an option for testing purposes, not really viable in a production environment. Ideally, though, you'll want to serve the web pages through the same nginx that's proxying websockets: in that case, when the user accepts the self signed certificate to open the page, websockets are automatically accepted too.
L.