Material Slot Order Completely Broken on Reimport Despite Clean Naming Convention (_skinXX Suffix Ignored)

[iZerat]

Hi everyone. I’m experiencing a frustrating issue with material slot ordering when reimporting skeletal meshes in UE 5.3.2.

Reimporting a character with 21 material slots (named 00_eye_iris_skin00 to 20_necklace_skin20). The “Reset to FBX” button completely ignores name matching and scrambles the slot order.

In Blender, I added the “_skinXX” suffix to the material names. In fact, after clicking “Reset to Fbx”, the material of the bone mesh will become messed up.

Is the name here correct, but the order of the elements in the array has changed?

Then, when I exported different FBX files to compare and troubleshoot the issues, I found that I couldn’t reproduce the problem.

This is very strange. What are the import specifications for material slots in Unreal Engine? Moreover, I also noticed that the “_skinXX” suffix that was originally used in Blender disappeared when imported into Unreal Engine. Is this the way the import process works in the engine?

I’m quite certain that there’s no issue with my material array. Is there any way to make the engine sort according to this array? The engine’s intelligent recognition seems to have a significant problem. It seems to identify based on the name of the material slot, or does it identify based on the specific material (material or material instance) filled in on this material slot?

And it seems that this window for matching the materials doesn’t have a cancel button either? If find that the import was incorrect, can only proceed by clicking “Reset to Fbx” or “Done”?

[iZerat]

I reproduced this problem again and gathered some new information.

The original material state of the grid was like this

Used the “Reimport”

The pop-up window looks like this.

Branch 1

After clicking “Reset to Fbx”, the result appears to be different from the original mesh.

Branch 2

After clicking “Done”, the material slots have increased further.

Branch 3

Without performing a reimport, and importing the fbx file in a new path, use the editor tools to copy the materials from the original mesh’s materials and set them on the newly imported mesh.

There is no problem at all, but this requires deleting the original assets and replacing the references. Such an operation is very cumbersome.