: Unusual urls being created - Wordpress site Hopefully someone might be able to help with an unusual problem that I have only just noticed - and it appears to have been occurring since at least

Hopefully someone might be able to help with an unusual problem that I have only just noticed - and it appears to have been occurring since at least Nov 2017 (the earliest cache date that I have found).

For example...

This URL has been generated/created - it seems that with (at least) two categories if I take a 'whole' URL and copy and paste that after the category part only URL then it will resolve... (and has been indexed!) ie (and note the latter part of the URL only has 1 '/' - as indexed by Google) although it also resolves if I change that to have 2 //
www.londontheatre1.com/shows/theatre-news/https:/www.londontheatre1.com/shows/theatre-news/page/250/
This is a duplicate of
www.londontheatre1.com/shows/theatre-news/page/250/
I think this has only happened with (archive) pages…

To make matters worse these URLs have been indexed by Google (there are several hundred of them and they are essentially duplicates of the archive page URL.

I have set up a staging site and deactivated all plugins and also activated Wordpress 2017 theme and the problem is still there.

Staging site is here - www.staging1.londontheatre1.com/shows/theatre-news/https:/www.londontheatre1.com/shows/theatre-news/page/250/
Any help gratefully received.