After building a WordPress custom front-end user profile, inserted the generated shortcode into a published page, we still need to inform ProfilePress about the page that contains the profile shortcode so it knows what page to use in rendering the front-end profile.
If this isn't done, users profile won't be accessible via the url
http://yoursite.com/profile/username where http://yoursite.com is your website username and username is a user's username.
See the succinct guide below on how to get it done.
Under Front-end Profile Settings section, select the page with the profile shortcode in Page with User Profile Shortcode and save.
To change the profile slug from "profile" to say "user", enter it to the Profile Slug text field.
Finally, flush the rewrite rule by navigating to Settings > Permalinks and clicking the Save Changes button.
When the profile url (http://yoursite.com/profile/username) is visited, ProfilePress will used the page that was set above to render the profile page.
To redirect WordPress author page of users to their front-end profile, tick the Convert Authors to Profile checkbox.