Featured Image is active, but thumbnails do not show up in Category archives

hi.i use kent theme on wp 4
home page it’s ok, but in category, all article’s don’t have a featured image. featured image works on homepage and the article page only.

i used <?php the_post_thumbnail(); ?> on content.php file on theme, and i make it work, but i have only 1 problem.
on category now, every image is real size, not thumbnail..it mess the website up with that rezolution pictures.

what can i do? thanks a lot!