When exporting a Static Mesh from within UE4 that has multiple materials, some of the material IDs will be condensed into a single ID which will mess up how the material assignment for that part of the mesh.
An example of this can be seen with the SM_Window from SunTemple that when exported will combine Elements 0 and 3 into a single element on reimport. (This asset has been attached here from 4.10 version, just place folder in Project Folder > Content)
Tested this in:
1. Download attached asset to project folder
2. Export the static mesh as FBX from UE4
3. Reimport the static mesh and overwrite or import to a new folder in the project
4. Assign the materials to the correct slots using the original as a reference
Results: Material IDs are condensed in some cases resulting in material UVs to not assign the material to the correct faces.
Expected: All material ID assignments should export and reimport correclty.
Head over to the existing Questions & Answers thread and let us know what's up.