This little function I created to see what happends when…
Outcome here was showing the excerpt as wished when filled out in backend and if left empty it keeps blank.
I have no idea why you have filter it that way but that is the way you wish I assume.
add_filter( 'get_the_excerpt', 'if_excerpt_left_empty_show_this' );
function if_excerpt_left_empty_show_this( $excerpt ) {
if (strpos($excerpt,'<!-- value') !== true) {
return $excerpt;
}
}
Maybe it helps a little? If totally incorrect, please do say and I will delete it.