As reported by a community member:

I tried to open a profile page of [[iwi]] or John Dethridge, but if I open it says "404".
John Dethridge: https://www.topcoder.com/members/John%20Dethridge
[[iwi]]: https://www.topcoder.com/members/[[iwi]]
Seems like user includes space, '[', ']', '(', ')' cannot open user page.

It looks to me, there are two problems: (1) username in the URL must be URL-encoded, (2) the user profile endpoint demands trailing /. These links work:
https://www.topcoder.com/members/John%20Dethridge/
https://www.topcoder.com/members/%5B%5Biwi%5D%5D/

The best fix will be to update the routing inside topcoder-app, so that it redirects to the proper profile pages even if the incoming link violates (1) and/or (2).