Issue in slug the url with mb_url_title

Hello,
There are a problem on URL Helper and mb_url_title in CI 4.x to create slug for URL.
When I'm on Arabic language and used these characters "ف" and "ح", there are a problem on hyperlink and when I want to clicked on the hyperlink that contain those characters the pages not found.
I didn't see this problem in CI 3.x and only this problem is in the CI 4.x
Regards,