Membership restriction incorrectly protecting pages with no records

Membership is great and appears to work perfectly.

I'm using it to restrict access to sections of woocommerce. As i don't have woocommerce categories to choose from I am using URL Groups.

However, I'm finding that pages that normally return 'no results' like gets the protected page. If there are events to show, then it works fine.

Another example, the posts archive: this page has results and works fine. However if you try - a month archive with no records, you see the protected page again.