Chances are if you have imagick turned on and enable in the store manager and your thumbs are not showing you are most likely getting the error "unable to profile image" from imagick. You will not see this error directly on the store front anywhere so you won't know if that is the error you are getting or not.
However to work around this you can disable color profies in the assets/includes/tweak.php file. You will need to open that file in your favorite editor (text editor) and modify a line in it.
Find the line:
$config['colorProfile'] = 'sRGB.icm';
Change it to:
$config['colorProfile'] = '';
Save your changes and then it should work.