I was having this problem as well. I checked a few other plugins that did something similar and noticed that if you open the class-public.php file in this plugin’s “includes” directory and change this line:
<img class="rfbp-image" src="<?php echo esc_attr($p['image'] . '?type=' . $opts['img_size']); ?>" style="max-width: <?php echo $max_img_width; ?>; max-height: <?php echo $max_img_height; ?>" alt="" />
to:
<img class="rfbp-image" src="<?php echo esc_attr($p['image']); ?>" style="max-width: <?php echo $max_img_width; ?>; max-height: <?php echo $max_img_height; ?>" alt="" />
It starts displaying video small thumbnails. Not sure if removing that bit of code is a good fix, but it’s passable for my purposes.