Within System > Manage > Plugins edit the "Community Builder System plugin" plugin and be sure both "Redirect URLs" and "Rewrite URLs" are set to "Enabled" as well as ensure the plugin itself is published and public access. These will redirect away from Joomla login/registration pages to CBs.
but it forces us to disaply that menu item and we don't want that.
Joomla lets you hide menu items from view. Under the "Link Type" tab set "Display in Menu" to "No" and it won't be visible anymore, but can still function. This is a great way to customize SEO without having a menu item actually visible too.