This message seems to occur once the sessions have timed out. However, the messages do not appear as a response to a request. It may make sense that a message is displayed if a request has attempted to access an invalid session, which could lead to an invalid swap (why that would be severe I do not know). But in this case, the message seems to appear once the session has timed out.
 Why is it even trying to swap in a session if there was no request? Why do that?
 Is this message harmless (see this discussion)
 If it is harmless how can I suppress this message.