Permalinks and trailing slash problem

Hi all,

I have this permalinks strucutre: /%category%/%postname%/

then all my url have a trailing slash.
I have changed an URL page from url-A to url-B. I can see this change on my sitemap.xml but now I can see on Google webmaster tools that https://www.mysite.com/url-A/ returns a 404…

If I try to access to https://www.mysite.com/url-A/ I get a 404 but if I try to access to https://www.mysite.com/url-A (without trailng slash) I get the content correctly.

What is the problem? why I loose the trailing slash in my old permalinks? how can I solve it?.

Thanks!