City inspection passed, HUD failed — how?

It confuses every new manager once: the city signed off last month and HUD's inspector just wrote a page of deficiencies. Different standards, different sampling, different definitions of the same word — a pass in one system never binds the other. Post your best example of the two systems disagreeing, and what you changed afterward.

The first time this happens to a manager it feels like a trick, but it is really two different questions being asked. The city asked whether the building met the local code on that day; HUD asked how the sampled units scored against a national standard with its own definitions. Neither answer predicts the other, and budgeting your prep off a city pass is the trap this thread exists to disarm. What's your best example of a city pass that HUD failed — and what did you change in your walks afterward?