Recent posts using the same slug

Hi everyone,
See the "Recent Posts" on the right of this page:
All pages have the same URL.

If you open a blog post, the widget will adapt its URLs to the current post.

Anyone encountered this before? It seems like a native WordPress bug. We don't know where to look to find a fix (we're devs).

If you need any extra information or access, let us know. We will create an administrator for you since the WPMUDev Dashboard doesn't work on native domain name mapping (we've been told).
Thank you for any help!