success="" attribute or Page Redirection Setting does not Redirect Users to the Correct Page
The success="" attribute, custom success url, will not work if the page that you're redirecting users to:
(1) has been given higher membership level restriction;
(2) is set it as a product, category, lesson etc;
(3) has been assigned as either welcome login page or redirection page.
You would need to remove these restrictions to avoid overriding the redirection function.