question

This is mentioned in the backwards compatibility notes of FlexSim 2024:

• Fixed imported values of Specular, SpecularFactor, and Shininess from FBX shapes.

Release Notes and History (flexsim.com)

Previously, those three properties were not being loaded properly from the file. Now that they are being loaded properly, any shapes that were relying on them not being loaded correctly are now displaying as you see.

The best solution is to fix the material values in the files themselves. Depending on your 3D modeling software, the material settings that affect those three properties may be named slightly differently. I adjusted our affected fbx shapes using Blender 2.79b. (Blender 2.8+ has a radically different material system that doesn't export to 3D shape formats as nicely.)

The basic gist of the change is that previously, the specular factor and shininess values were massively large, which leads to a tiny specular highlight (shiny shoes have very small highlights). Now that the correct values are being read from the file, the highlight is a lot wider (less shiny), which is why the specular color seems to now dominate the final output color.

To fix it, you'll want to lower the specular color value (from bright white to dark gray or to the diffuse color) and/or adjust the shininess/strength values to be higher (to get a smaller highlight that isn't spread all across the surface).