Accessing Custom Fields/Meta Data

I’m working on a client’s site (link) and have discovered that I can’t access meta/custom field values I’ve manually assigned to a download. The fields are being set correctly, and I can see that they exist in the wp_postmeta DB table when I search for the download ID. (Screenshot of DB search results: https://i.imgur.com/XkkwkuD.jpg)

I can work around this using the Short Description on the actual download page, but on the parent “Podcasts” page, I’d like to display the custom field keys/values for the podcast duration and recorded-on date.

The code I’m testing with:

$duration = get_post_meta($id, 'duration', true);
$record_date = get_post_meta($id, 'record_date', true);
$thumb_id = get_post_meta($id, '_thumbnail_id', true); // Test
$meta = get_post_meta($id);

The “duration” and “record_date” variables are empty when echoed on the page:

Duration: <?=$duration ?>
Date: <?=$record_date ?>
Thumb ID [test]: <?=$thumb_id ?>

==

Duration:
Date:
Thumb ID [test]: 7579

My print_r($meta) results:

Array (
    [_thumbnail_id] => Array (
            [0] => 7579
            [1] => 7579
        )
    [_wpt_short_url] => Array (
            [0] => 
        )
    [_wp_page_template] => Array (
            [0] => page-download.php
        )
    [_dp_original] => Array (
            [0] => 7530
        )
    [_edit_lock] => Array (
            [0] => 1507152808:2
        )
    [_edit_last] => Array (
            [0] => 2
        )
)

Is there any chance or reason DLM might be disallowing access to custom fields? I hope I’m not missing something obvious. Any help you can provide will be amazing!

The page I need help with: [log in to see the link]