This may happen due to the specifics of subscription products. If you manage products concurrently using the API and the portal, then the following may have happened. You created a product object through the API and then bound it as a renewal product to the product that initiated the subscription.
In such a case, you can view a renewal product through the portal at the first step. However, after that it is no longer displayed as a separate product. You can view its properties in the product that initiates a subscription.