Totally unrelated user sessions are getting a login name from a separate user session jammed into them.
Product defect. This problem has been identified as CR0233317. This problem results from hits from multiple clients being proxied onto the same TCP connection. If a hit contains a login name BUT does not contain a session id, then that login name will be associated with the next hit that has a session id.
Issue fixed in version 184.108.40.206. The latest version of Foglight Experience Monitor can be downloaded here.