The reset password and retrieve username features have been refactored to stop using wiki pages to work. The rationale is that these pages needed to be viewable by the guest user to work, thus making it impossible to protect the full wiki to guests (among other problems related to rights on these pages). Thus they have been re-implemented using dedicated URL schemes and components, and thus have had their URLs changed:

• Reset password:
  • New URL: /xwiki/authenticate/reset 
  • Old URL: /xwiki/bin/view/XWiki/ResetPassword
• Retrieve username:
  • New URL: /xwiki/authenticate/forgot 
  • Old URL: /xwiki/bin/view/XWiki/ForgotUsername

The old XWiki.ResetPassword and XWiki.ForgotUsername wiki pages must not be used anymore, and any custom change perform in those pages won't be taken into account (you'll need to port your changes to Java since the new feature is coded in Java). However, the pages have been kept to ensure that using the old URLs will keep working for the time being: the pages now redirect to the new URLs.