First off, it’s the WooCommerce plugin that’s controlling the sizes of the images displayed. Then, the warning “Properly size images” triggers when the rendered image is 4kB greater or less than the actual size of the image. Unless the images are properly sized and well optimized, this warning will always trigger.
The rendered size of the images with the issue is just 170 x 96px.
You can try adding this PHP snippet and see how it goes: