For the browse_favorite method your code doesn't contain the main argument - the profile_id of the person who views the Favorite people block. In this state, your code gives the error 500. You may pass the 0 then UNA will insert the id of the viewer.

So it should have the look like:

array (
 'module' => 'bx_persons',
 'method' => 'browse_favorite',
 'params' => 
 array (
  0 => 0,
  1 => 
  array (
   'unit_view' => 'showcase',
   'empty_message' => false,
   'ajax_paginate' => false,
  ),
 ),
)