Why do you see this error:
When a browser connection is upgrading from a HTTP (comet) transport to websockets, this is logged by the client library from time to time when some operations are performed on the older transport.
What can you do to resolve it:
If you only see it in the logs, you don't need to worry about it as it won't affect your app in any way. However, if you get this error as a response to a request you've performed, please get in touch with us with the relevant info and logs and we'll be happy to look into it for you.