update_post_meta Not Processing Array Data (Not Sure What I Am Missing)

$post_id is never defined in any of your update loops, and this shows that a simple single loop is not enough to achive this.

Since you are looping two concurrently created arrays, you would need to do something like this instead, using the index to match values:

for ( $i = 0; $i < count($post_ids); $i++ ) {
    update_post_meta( $post_ids[$i], '_metadescs', $metas[$i] );
}

Alternatively you could do a loop within a loop and match the index this way:

foreach ( $post_ids as $i => $post_id ) {
    foreach ( $metas as $j => $meta ) {
        if ($i == $j) {update_post_meta( $post_id, '_metadescs', $meta );}
    }
}