When importing Gridded Items from Counterpoint into Magento, let's say "Men's Graphic Tee", one Configurable Product is imported ("Men's Graphic Tee"), and several Simple Products are imported ("Men's Graphic Tee | Blue | Medium, Men's Graphic Tee | Red | Large etc.). When the items are imported only the Configurable Product is tagged with a Category attribute. When a customer buys one of our shirts, they don't buy the Configurable Product, they buy the specific Simple Product that they want. So if we have a promotion going for 30% off category "TEES", the item that gets put in the customer's cart actually isn't part of the category.
Instead of creating promotions filtered by Category for gridded items, try using a different identifier attribute such as the Category ID which can be uploaded from Counterpoint. Read our knowledge base article on adding product attributes to be used as promotional filters.