3D GEN not displayed as filled surface in 3D Tool - Forum - iMOD

Hello All,
For using HFB I created an ascii 3D gen of a dike conform syntax in the manual (page 681 of manual; 3-D Polygons).
Problem: In 3D Tool the 3D GEN file is not displayed as a filled surface (only the outline is displayed).
To reproduce this problem I attached:

• a demo version of the gen file (Dijk_3D.gen);
• belonging extent / elevation map as idf file (DIJK_3D_TIF_1.IDF);
• print made in 3D Tool (Dijk_3D_30_september_2021.jpg).

iMOD manager, Overlays, DIJK_3D.GEN, Legend, Lines and Symbols, Fill Polygons, check box, Apply: Has no effect.
Question: How to fill the surface of the 3D gen?
Thanks in advance again.
Martin