Creating a new page sends me to /$url once trying to visit it!

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Hi
concrete5 5.6.0.2 installed.
was working fine until now
Nothing specific installed (apart from a custom made theme and the nd php block)
when we add a page (from the full sitemap, or adding a page from another page), and then we try to visit it, we end up on /$url (which of course gives a 404 error)

the page is correctly set in the database (it seems...)

we have tried to reupload the contrete forlder from 6.5.0.2, still no luck.

any idea?