> 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?

Without necessarily endorsing the article's ideas....I took this to be like the diamond-inheritance problem.

If service A feeds both B and C, and they both feed service D, then D can receive an incoherent view of what A did, because nothing forces B and C to keep their stories straight. But B and C can still both be following their own spec perfectly, so there's no bug in any single service. Now it's not clear whose job it is to fix things.