> Even without a directed cycle this kind of structure can still cause trouble. Although the architecture may appear clean when examined only through the direction of service calls the deeper dependency network reveals a loop that reduces fault tolerance increases brittleness and makes both debugging and scaling significantly more difficult.

While I understand the first counterexample, this one seems a bit blurry. Can anybody clarify why a directed acyclic graph whose underlying undirected graph is cyclic is bad in the context of microservice design?