I think it is a WP 4.3 issue. Doesn’t seem to matter what theme you use, or what browser. Gotta learn where the browser refresh button is :-(.
So far, I think 4.3 is close to a disaster for a WP major release. Lots and lots of issues – will crash or swamp some servers in some applications with cron bug. Has tons and tons of issues with plugins and themes now issuing all sorts of error messages (that most people won’t see because of wp-config.php settings). And apparently this dashboard menu issue.