the_post_thumbnail doesn't resize properly

I am using the_post_thumbnail and when I do the image will not resize properly. It retains the height so it just squeezes down until the media query kicks in. When I just load the image via my cdn it works perfect. This is only with the post thumbnail. I have tried setting the image size via functions.php file and then loading in the name…..but still the same.

Any suggestions? Thank you