Reimport FBX will loose all materials

Hello all.
Working since 2 weeks in Unreal for a test project i´ve some very strange problems:

Have a bicycle-element imported as skeletal mesh (FBX 2016) with some material-slots inside. The client is changing very often the model itself or the materials. All Elements are directly animated in XSI (or Maya), then animation baked and exported.

Step 1.) Imported into Unreal with “File import into Level”, because i want to reimport these FBX files and need it in one mesh:

Step 2.) Mesh is inside Unreal with all animations and all Materials from Maya ( i change it with UnrealMaterials later) as you can see here:

Step 3.) Client will changes in animation, do it in Maya, export it again (without changing materials) as FBX, klick in Unreal on the purple FBX SCENE IMPORT DATA for Reimport the FBX file:

and then BOOM: all Materials are grey in viewport. All Materials are still there and present, but all Models are Grey:

I cannot assign any materials, even if i create direct materials in Unreal.
And this will happen with every FBX that i´m importing into Unreal, also simple Cubes from FBX: after the second reimporting of the FBX-File everything is grey and i can´t no more assign materials. What i´m missing here ?

1 Like