During the initial configuration of the Katana to BigCommerce integration, you can choose whether to import custom items on BigCommerce Sales orders to Katana.
If switched ON, BigCommerce custom items will be created as products in Katana. A new product will be created for each custom item, and custom items are not matched to products existing in Katana.
If switched OFF, custom items will not be imported to Katana and will not appear on Sales orders synced from BigCommerce.