??
In my case the category is ‘cars’ and the posts slug is ‘ford’.
I have ‘/%category%/%postname%/’ in the permalink option, and nothing in the one below it.
The page it is happening is here: https://www.housebuyingguide.co.uk/ The two posts I have got are just under the picture. You can see that the main title link, and the comment link have this problem, but the ‘posted in’ links work fine. (Though these seem to be of the form /category/cars/ford/’ – i.e. have the virtual folder ‘category’.)
It is possible I have buggered the WP code ?? But I have kept all my modifications in my theme, so havent messed with the actual code…