Hi Raymond Dowe,
I have replied to the support thread you have submitted on the issue earlier, but it looks like I've missed this thread. The strange thing is that even group pages with content pages under them display that problematic behavior, as by default only an empty (group page with no content subpage) group page will not be displayed in the navigation. Of course, the Show In Navigation property is also an important setting, however, I believe you have that one configured properly. One last thing to check would be the permissions set applied to that group page, I'd kindly ask you to check whether the page is included in the navigation when you're viewing it as an admin user.
Can you please try setting up a new group page and a new content page as its child, and check whether they'll appear in your navigation? Also, does this issue reproduce with one of the built-in navigation widgets placed on a new page? Looking forwards to your reply.
the Telerik team
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