Hi Christian, I am experiencing a very similar issue after moving from X17 to X18.
In X17, I had my concrete fills set to black concrete hatching on a green background, and Auto Detail produced that appearance automatically. With the same template in X18, the concrete fill I checked in Floor Structure still appears green, but running Auto Detail in a new cross section produces a white background.
On one generated CAD polyline, we found that the background colour source was set to Use Background Color. Changing it to Custom Color and selecting green corrected that individual shape, but that does not resolve the automatic behaviour for future Auto Detail runs. The generated concrete pattern spacing was 50 mm.
Has anyone found a setting or a template migration issue that explains this? I would appreciate any guidance on preserving the assigned concrete fills automatically in X18 rather than editing each generated shape manually.
Chief Architect Premier X18, build 28.2.1.14, Windows. Thank you for raising this question.