In my case, they've always been associated with a prior version of the browser I've been using (legitimate and never phony). Sometimes the browser's signature changes and the update version is added. Eventually the older version does in fact expire and generate the notification. Unfortunately the notification fails to identify the "device" expiring. Unless you actively monitor the trusted "devices" it's difficult to determine that.
In addition, clearing the web site's cookies can lead to trusted devices becoming unsynchronized since the implmentation is cookie based.
Just informational, it's an annoyance for most of us; however, Visible's implementaion does appear more problematic than others I encounter.
