Are your temps the same in each room. Humidity is Relative to it. The humidity changes, and lowers as heat rises. Then when the room cools the humidity will rise. Less numbers or smaller plants mean less expatriation from the plants also, they suck that water up and breath it out like a dog pants to get rid of heat.
Is your air being drawn in, coming into each room separately, or one then the other. Last year I ran my air from my veg tent, through my clone cabinet, and exiting that, saving me having to use another extraction fan, and heater at night, but the controls only covered the veg tent, so sometimes it was good, sometimes it wasn’t, depending on how much heat, and moisture was being vented.
That’s why its important you try and keep your lights, on, off temps, in a max of 10 degrees F difference between lights on and off. It helps avoid a big swing in your relative humidity, and lessons the chance of PM.