I thinks it has been resolved !
Problem resolved,
I haded this after le update_field method :
if ( isset( $_POST['acf']['field_5a68a6dda4b03'] ) )
unset($_POST['acf']['field_5a68a6dda4b03'] );
And mostly I correct the false variable name $new_user and not $news_user.
So dumb !
Yes please, could be really handy ! Thx