I was having a problem with my categories not showing all of the products when I used the BigCommcerce shortcode. I did some digging and it looks like the GetProducts function was only pulling the first 50 products from my BigCommerce store. My category products didn't happen to have any products in the first 50, so the category list returned empty.
I've come up with some replacement code that I think will fix the problem. In the interspire-bigcommerce/lib/class.api.php file, replace the GetProducts function with:
This seems to work for me but let me know if you see a problem with it. Thanks!