When importing an asset that is using the naming convention for SkinXX to order material elements does not work properly when the elements are not sequential. Any material that is not in sequential order will not be imported.
Test asset with non-sequentially ordered materials using the SkinXX naming convention has been attached.
1. Created simple box asset in modeling application
2. Assign multiple materials named using the SkinXX naming convention to the material
3. Make sure the material names are non-sequential (ie. Skin00, Skin91, Skin25)
4. Export asset to FBX
5. Open UE4 and import with import materials/textures enabled
6. Open asset and look at material elements list.
Results: Only assets with sequentially ordered numbers will be imported from 0 - XX, while other elements will be ignored.
Expected: All material elements should be imported.
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-25928 in the post.