Or more specifically, showing up in IR but not in offline. They show up in IR, but don't show up in offline in the VFB, using Render View, Interactive Render Region in the view (and in both view cases, the smoothing on the geometry doesn't render either but that may be a C4D thing?).
The Picture Viewer actually shows whatever the Corona VFB shows - that is, if you use IR in the VFB, then the PV shows the textures. If you use offline in the VFB, the PV does not show them.