actually, now that I took a better look, there is indeed a cblogin module but it's the omni-present one that is in my header position. I think most people would expect one in the component area. Also, without the error showing until you click another link, all of the users have no idea what to do.
I also noticed this doesn't happen if the user is presented with a direct-to-article link such as this:
httpx://www.site.org/index.php?option=com_content&view=article&id=333
Using the above link does display a cblogin module in the component area and then the user is taken to the correct URL after login.
It seems that this is only happening when the user is given a menu URL to click on and not a direct URL.
This is the URL that causes the issue:
httpx://www.site.org/key-dash
that URL is a "single article" form Joomla. The menu item is set to restricted as is the category, and article itself. Also, the article is actually #387, not 333 so not sure where CB is getting itemID=333 from (?)
CB 2.3, CBsubs 4.3, PHP 7.1, J! 3.9.X