We have different static mesh assets with an amount of materials (eg: 4 materials x 3 lods = 12 total) but If we pose this static mesh in scene the staticmeshactor will have an extra 13th material! (index 12)
Also the materials from lod1 to n-1 are set as WorldGridMaterial in the statichmesh preview and set as like the lod0’s ones inside the staticmeashactor detail panel.
Hello drowne -
We are tracking two issues with the Material Slot numbers as they appear in the Viewport Details Panels. UE-12931 where an additional Material Element is created when resetting the Element in the SM Editor and UE-1394 where reimporting can add and not overwrite material slots. Of these two issues can you see if one or perhaps both are causing your actual issue.
If neither seems like your issue, a copy of your mesh would be helpful in tracking this down further
Let me know -
Eric Ketchum