User blog comment:Rappy 4187/Technical Update: November 9, 2015/@comment-25648422-20151111155426/@comment-1251315-20151111200035

That happens to me if I hover over the notifications before the page has fully loaded. A refresh fixes it, it'll be because the notification JS isn't loaded when you hover over it. Wikia could easily make it so that, if the JS is not available, that it keeps trying to load the JS until it's available.