The down arrow which appears when you hover over certain UI elements (such as a job in the Build Queue, or the job number of a running job) gives you access to a context menu, e.g. to run a job in the job queue immediately, or to see console output of a running job.  This down arrow appears only once for the first UI element you hover over.  But if you try to hover over another UI element no arrow will appear.

A workaround is to refresh the web page with F5.  But this only gives you access to the down arrow by hovering over one UI element.  You'll have to press F5/refresh each time you need to do this.

Impacts Firefox on Windows.  I haven't tried other web browsers.