Check which renovation filter you have active in the plan view.
If that is not it maybe the walls are on another storey.
Or maybe you wall display is set to "Cut Only" and your Floor Plan Cutting Plane is set above the walls.
Or it could possibly be that the layer is turned off in the plan view but is turned on in the 3D view.
Another possibility is the Partial Structure Display set for the plan view - but then I would not expect to see the dimensions either.
One of the forum moderators.
Versions 6.5 to 25
Dell XPS- i7-6700 @ 3.4Ghz, 16GB ram, GeForce GTX 960 (2GB), Windows 10
Dell Precision 3510 - i7 6820HQ @ 2.70GHz, 16GB RAM, AMD FirePro W5130M, Windows 10