As calawide send me his failing files, here are my report about them:
- The Tinkercad MTL file is wrong because the line starting by illum is supposed to be followed by an integer not a decimal number (see MTL specifications)
- The 3D Builder OBJ file is wrong because the lines starting by v are followed by 6 numbers not 3 or 4 numbers (see OBJ specifications).
Please report these issues to the teams of each software.