[MRM]

It's condensation. For some reason the air flow is bringing the warm moist air from the bath, kitchen and rest of the house into that section of the hall bath. It's just a quirk of how your HVAC system came together. There's nothing wrong with it, you just need more ventilation in the area.

People consume hundreds of gallons of water every day. Everything from bathing and drinking to cooking and breathing. I've seen the data on how much water vapor an American puts into the air just in his daily life. I don't remember what the specific numbers were, but it's remarkable. For some reason the air currents flow into that area and it gets more humid there than anywhere else. Being summer in SC doesn't help matters.

The house probably needs a whole-house air exchanger if it doesn't already have one. If it does, it needs adjusting. But just get a better fan in that area and the problem will go away.