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@ xevo: Yup, I had removed kubrick but, even after putting it back in and making sure it was activated, still nothing. The blogs do show up in the Blog Directory and the blog listing of my admin dashboard, but nothing else associated with them seems to exist; no blog, no blog dashboard…

OK stop.

After much fiddling, I just found the problem (another duh! moment). I had a chat plugin activated site-wide which, somehow, had prevented any blogs from showing up. Deactivating and reactivating (not site-wide this time) solved it.

Thanks again for your very quick reply!