What is the difference between $variables['elements']['#node'] and $variables['node']? Just wonder what is the difference between $variables['elements']['#node'] and $variables['node'] in hook_preprocess_node(). Are the same instance of the same node?
See the code executed in template_preprocess_node(), the function called before the preprocess functions implemented by modules for a node.

$variables['node'] = $variables['elements']['#node']; 


So, yes, $variables['node'] and $variables['elements']['#node'] contain the same value.