I had the same issue, main users have the contributor role and a simple sidebar comment sidebar widget was not working when logged-in! Strange. I solved it by some sql:
function getLatestComments ( $postid ) {
global $wpdb;
$sql = "SELECT * from $wpdb->comments WHERE
comment_post_ID = $postid AND
comment_approved = 1
ORDER BY comment_ID DESC";
return $wpdb->get_results($sql);
}
I used this instead of get_comments. You may modify the sql and customize as required.