Material slots are combined into one 'default' material after importing

Hi talents,

I get problem during mesh importing process: there were supposed to be 4 material slots, but they merged into one ‘default’ material… I am using Clo3d (similar to Marvelous Designer) for creating garments. First I thought it could be the export setting issue, but the mesh and material slots works well in Substance Painter. I also tested the same exported mesh in Blender and C4D, and everything is OK.

Can anybody please help to see if the problem can be fixed? thank you very much!