Help with understanding air leak in wall cavity – GreenBuildingAdvisor

There is a closed cavity outlined in red that has plumbing for a tub. The cavity has six sides.

-The top is covered with wood and the edges where the wood meets the framing is foamed

-The bottom is the subfloor. The exterior facing edge was foamed

-One side is exterior wall facing and has thermaply that was foamed around the edges (in the picture the thermaply hasn’t been fastened or foamed yet)

-The other three sides have drywall. One of the sides has plumbing coming out of it over a bathtub.

When running a blower door, there is a strong draft coming out of the valve trim. I’m having trouble understanding why this would be the case since it seems like all the gaps in the cavity were foamed, including plumbing penetrations.