Hello,
I saw the screenshots you attached and visited the URLs you provided. The product images are controlled by WooCommerce itself and our theme doesn’t influence it. You can find the settings under Appearance >> Customize >> WooCommerce >> Product Images.
In your case you have set the main image width to 600px means that it will crop 600px image from the image you added as the main product image. It is working for the image that is bigger in size because it’s cropping the area from it.
And the other images are smaller in size as you set the main image width that’s why they are not working. Please use images of bigger size that will fix the issue.
I hope my above explanation will be clear enough for you to understand the working.
Best Regards.