Check everything Under - View Tab > Graphics > Visibly Graphics > Railings - is turned on
To check this use a default Railing style and see if the issues repeats, if not you need to look at your Railing Family Setting.
You can copy a railing from an Architectural Revit Template and Paste into a Structural Model as there are limited Railing System Families in the default Revit Structural Template and only has the Top Rail Shown

Architectural Railing

Jay Colcombe
Autodesk Certified Instructor
Revit Architecture & Structure Certified Professional
AutoCAD Certified Professional
B.Sc. Hons Civil & Structural Engineering
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