Require agreement to terms on membership renewal

I did that and see the same thing.
On the registration page, there is a link to open the interpreted URL in another tab. By interpreted, I mean that it took the URL you recommended and translated it into the hidden menu item URL.
On the renewal page, there is an iframe instead of a link, and the URL is the home page

My guess is your article isn't accessible then. Your article should be published and public. It either should be in no category or the category it's in also needs to be published and public. The menu item associated with the article should also be published and public. That's the only reason I can think of for Joomla's routing function to convert it to a home page URL.

If your issue still persists after checking all that please PM backend super user login credentials and will take a look.

I checked all of this: hidden menu item, article, and category. All are published and public.
Will PM you credentials.

Have reviewed your install. You've CBSubs configured to use the same terms and conditions as core CB. For this it uses the core "acceptedterms" field. You're using a custom terms and conditions field "cb_acceptedwaiver", which CBSubs doesn't integrate with. So you either need to configure and use "acceptedterms" or you need to set CBSubs terms and conditions to "Ask to approve different terms and conditions for checkout", which will let you supply the WYSIWYG HTML and text for whatever you like for the terms display.

For now I've edited the "acceptedterms" field and adjusted its settings to match your "cb_acceptedwaiver" field configuration under the Parameters > Display tag so it'll be functional in CBSubs, but it's always recommended to use "acceptedterms" for your main terms and conditions policy.

Thanks so much.

In implementing this, I ran into a problem. We have two different T&C docs.
I can do this for renewals with "Ask to approve different terms and conditions for checkout" with some text that has links to the two docs.
But I don't know how to do this with acceptedterms as it allows only URL or text. Can the text include HTML links?