Exclude Post Format from Next/Previous Posts

I am trying to modify my previous/next post navigation on a custom post type page. I want to exclude the “Link” post formats from the navigation, so only standard posts are included, but I can’t seem to get it to work. It works perfectly otherwise.

Here is my code:

<?php // Previous/next post navigation.
$next_post = get_next_post();
$previous_post = get_previous_post();
the_post_navigation( array(
    'next_text' =>  get_the_post_thumbnail($next_post->ID,'thumbnail') . '<h4>' . __( 'Next Project:') . '</h4> ' .
        '<h3>%title</h3>',
    'prev_text' =>  get_the_post_thumbnail($previous_post->ID,'thumbnail') . '<h4>' . __( 'Previous Project:') . '</h4>' .
        '<h3>%title</h3>',
) ); ?>

I have also tried using the previous/next_post_link query, this one shows nothing at all when the in_same_term variable is set to true:

<?php previous_post_link( '%link', 'Previous project: %title', TRUE, '', 'post_format' ); ?>
<?php next_post_link( '%link', 'Next project: %title', TRUE, '', 'post_format' ); ?>

Anyone have any suggestions? This is beyond frustrating.