Production WebSocket connection failed: Unexpected response code: 400

As in the title described my production app cannot connect with the web socket.

WebSocket connection to 'ws://mywebsite.tld/sockjs/771/6wzzgr6y/websocket' failed: Unexpected response code: 400

The interesting thing is, that the app still works 100% as expected.

My question now is: is my app using a fallback or something in order to work or do I have to fear, that this 100% running thing is just my impression!?


using a local wscat also returns 400:

meteor wscat --connect ws://mywebsite.tld/websocket
error: Error: unexpected server response (400)