At this line $wp->query_vars['protected-iframe'] won't be defined on edit.php page or any post request page. It is throwing wp_die() on those pages. I know it is used for redirect rule and iframe loading support but parse_request gets called on all page having post.
https://github.com/humanmade/protected-embeds/blob/master/protected-embeds.php#L170
At this line
$wp->query_vars['protected-iframe']won't be defined on edit.php page or any post request page. It is throwing wp_die() on those pages. I know it is used for redirect rule and iframe loading support butparse_requestgets called on all page having post.