Hybrid ASP (H-ASP) is an extension of ASP that allows users to combine ASP type rules and numerical algorithms. Dynamic Remarketing Ads is Google’s platform for serving customized ads based on past interactions with a user. In this paper we will describe the use of H-ASP to diagnose failures of the automatic whitelisting system for Dynamic Remarketing Ads. We will show that the diagnosing task is an instance of a computational pattern that we call the Branching Computational Pattern (BCP). We will then describe a Python H-ASP library (H-ASP PL) that allows to perform computations using a BCP, and we will describe a H-ASP PL program that solves the diagnosing problem.