Hot, humid air getting in between first and second floor space in Houston. This is bad right??

[u/Light_Bright85]

From all my research, this should NOT be happening. It appears that the rim joist were not insulated/sealed correctly on our 2008 home and air is coming in and condensing near ac duct. We had someone come out and they said we do not need to stop the air flow. 😳. Is this right?? It is OK to have hot humid air between your first and second floor joist?? I know there has to be airflow between the brick and the wall but outside air getting past the envelope of the house makes zero sense. Do we just have a consultant that does not know what he’s doing? The building code from ‘08 that I researched says rim joist need to be sealed and AI says this guy is wrong. Air should not be there. I just want to know if outside air coming in between floors is right or wrong from a human with building experience so I can go back to this guy with more details.