hi
this event call by wrong params in inc\users\views\_user_identity.form.php
it must be
$Plugins->trigger_event( 'DisplayProfileFormFieldset', array(
'Form' => & $Form,
'User' => & $edited_User,
'edit_layout' => 'private',
'is_admin_page' => $is_admin_page,
) );

& $Form and & $edited_User is correct params