You may encounter this issue when the Walls category is not visible in the view.
Symptom: Curtain wall elements in your model are not visible even though the Curtain Panels and Curtain Wall Mullions categories are set to visible in the view.
Issue: A curtain wall belongs to the Walls category. The curtain panels and curtain wall mullions that comprise the curtain wall have their own categories but are not visible if the Walls category is not visible in the view.
Solution: Override the visibility of wall elements individually, or use a filter to control visibility of curtain walls separately from other walls in the model.