I have a page with slug “blog” and CMS collection with slug “blog”.
And my structure looks like ‘example.com/blog’ and ‘example.com/blog/some-blog-post’.
It was working, but now I get an error “Collection with this URL already exist” and can’t make any changes in page settings.
I didn’t change slugs. Why I got this problem?
Here is my public share link: LINK
(how to access public share link)
Same problem here.
This problem just came up today… Before today this was possible…
I also get this error (“Collection with this URL already exists”) when I want to use a url that I once used but was renamed a few hours ago.
In my example I created a CMS Collection with the url ending of “programm” and changed it to “konzerte”, now I can’t even create a page or folder called “programm”, even if there is no CMS Collection using this URL.
Is this a bug?
Okay I just fixed it somehow, but only to a certain point…
Fist I unpublished my site, then I renamed most of my pages and CMS Collections and then renamed them to the exact same names they had before.
After That I published the site again and I was able to create pages and folders with the wanted name.
But now when I open the folder that I just created it showed me the error message again. So as long as I dont have to change anything on the folder settings, I should be good to go 
I have had the same issue before but have figured it out with a new website. I created a new CMS collection with a slug like /installation-in/ and then also created a page called /installation-in/
I had not published either the webpage or the CMS at this point. It allowed me to create the page after I created the CMS collection and it all worked fine.
I tested it out and it seems to work fine. So like Martin said maybe it is to do with pages not being published first or around renaming.
Follow this trick to make it work:
