Magento - 在结账时没有显示最近的商店

I'm a total noob and this is my first time working with Magento 1.9.3.2

A webshop uses a onestepcheckout shopping cart (http://onestepcheckout.com/). And on the checkout page it can show your 4 closest stores based on the postal code that people fill in. However, for a couple of addresses, the actual closest store doesn't show up.

The weird thing is; it does show up in a checklist menu before you add the item in your shopping cart on the product page.