Water dripping from the ceiling over a humidifier
I bet your ceiling is cold.
Consider my cold drink on a hot day.  Humidity has spread around the clubhouse.  The outside of my glass is dripping wet and I must use a coaster.  Why does the humidity stop just on my glass and not breeze on by?  It is because my glass is cold, and passing humidity that bumps into it condenses into water.
So too your roof.  You have a cold spot for whatever reason.  Ambient humidity in the house stops there and condenses.  You could try to address the spot, or give up on humidifying the great room and concentrate on humidifying bedrooms.