When a ventilation system is out of balance, the airflow is not shared evenly, so you can get odors or air from one area entering certain spaces while others don’t notice it. If only one apartment in a row reports odors, that points to a localized pressure difference or leakage path that’s drawing in odor from bathrooms or kitchens into that unit. It’s a telltale sign that the system isn’t distributing air evenly across the line. The other patterns don’t fit as clearly. If every apartment has the same odor, it suggests a more general source or a building-wide issue rather than an imbalance between units. Odors that are stronger only on the top floor hint at vertical pressure differences or stack effects rather than a horizontal balance problem. Increased humidity in all units indicates moisture control or humidity sources rather than an imbalance in how the ventilation distributes air.