Ok, I think I figured where the conflict was on my end by starting with a fresh WordPress install and slowly recreating the conditions of my site.
The tab appears to not work in WordPress Multi-site installations with the “WordPress MU Domain Mapping” plugin installed where a different domain or subdomain is mapped to the specific individual site. (This only happens on any site except the 1st site of the Multi-site installations because you can’t map another domain or subdomain to the 1st site).
To fix it:
“Redirect administration pages to site’s original domain (remote login disabled if this redirect is disabled)” needs to checked on the Domain Mapping setting page of “WordPress MU Domain Mapping” plugin.
I originally unchecked it because the Headway Theme visual editor doesn’t work from the admin panel with it checked.
