“Ghost” Mullions in IFC Export

When I export an IFC file from Revit, I get’ghost’ mullions that are not modeled in my Revit model. I created a curtain wall mullion schedule in Revit but couldn’t locate these ghost mullions through their IFC GUID. I also copied the entire curtain wall and pasted it 10 meters away from the building in Revit and exported to IFC again. The copied version of the curtain wall does not show the ghost mullions. Does anyone know why this is happening?