@Anonymous
First thing to check if there is a light source defined...Edit the family of the lighting fixture and make sure the lighting source have been defined (if there isn't, define one and constrain it properly)
If there is a lighting source already defined...you should note that lighting fixtures are classified under two family categories (in Revit libraries you find them under Architectural and MEP). The difference between the two is:
- Architectural / Wall Based families (are Pre-Hosted)
- MEP / Face Based Families (are Non-hosted and when you place you are given the choice to place it on a workplane, A Surface or the vertical surface of a wall in in plan view)
If you are using Architectural/Wall hosted, it could be that the Placement Origin is defined at the center of the geometry rather than the face of the wall. And the reference plane defining that origin is constrained to the center of the wall => when the wall section increase, it hides either/or both the geometry and the lighting source.
- In such case, edit the family and make sure the geometry as well as the lighting source is constrained to the proper reference planes locked to the wall face

In Face based families, the placement origin is mostly defined by the reference plane locked to the surface. But sometimes, namely when people convert the wall based to face based without taking the above into consideration. Hence, you will need to edit and do the same procedure mentioned above
