has_post_thumbnail() not working

Assuming that you’re in The Loop, you can fix this problem, by replacing:

if ( has_post_thumbnail() ) {
     // do a bunch of stuff
}

with

$featured_image_url = wp_get_attachment_url( get_post_thumbnail_id( get_the_ID() ) );
if  ( ! empty( $featured_image_url ) ) {
     // do a bunch of stuff
}