Is the link you're trying to send them to protected by CBSubs? If it is and the content has Public view access level then CBSubs attempts to send them to the plans page to subscribe to access the content. If not logged in it will ask them to register. That's how that protection works. If you don't want that then set the view access level for the content to Registered and you should have normal behavior as before. Also ensure CBs system plugin within Extensions > Plugins is published, public, and ordered as the first system plugin with CBSubs system plugin just below it.

Set the menu item to Registered and protect it with CBSubs Content. If they're logged in they're sent to subscribe if not subscribed. If they're not logged in they're sent to login due to normal Joomla access denied behavior. That's the only way to have that behavior.

You should be able to create a second menu item that's a menu type of menu alias that links to your protected menu item. That might work how you're wanting as the menu alias is public and visible on your menu, but it links to a menu item that's marked Registered so in theory should send them to login otherwise if they have access it should send them to that menu item fine.