Not all material elements are created and assigned to the static mesh using multiple materials. With the attached mesh, only the first element is created and the other two are left non-existent. I can add them manually via the static mesh editor, though.
Workflow to create this asset:
NickBB and MattK, in an email discussion, brought up using the test assets that QA uses from Engine/Content/NotForLicensees/QA/FBX/StaticMesh/. When I checked the multi-material mesh "StaticMesh_18_MatIDs.fbx" this FBX works without any issue and creates all the material elements. I've attached that test asset here as well if needed for comparison.
This is a regression from 4.14.1 to 4.14.2, likely to do with the integration of fix for [Link Removed] that was causing a crash with multiple material ids.
Working: 4.14.1 Binary CL-3224400
Broken: 4.14.3 Automated Binary Build CL-3248269
Broken: 4.15 Automated Binary Build CL-3247232
Broken: 4.16 Dev-Framework CL-3248251
1. Import the attached asset MultiMatBox.fbx
2. Use Default Settings
3. Open the asset in the Static Mesh Editor
Results: Not all Material Elements are created that have assignments to the mesh.
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-40298 in the post.