Material Function Instance does not validate

Summary

With the v25.20 update Epic Games exposed the Material - Advanced - Material Function Instance feature, but ever since this feature never validated. It’s possible to create material function instances and override material parameters, but if such a material function instance would be used in a material, the project will stop validating.

Please select what you are reporting on:

Unreal Editor for Fortnite

What Type of Bug are you experiencing?

Other

Steps to Reproduce

  • Create a material function with an exposed parameter

  • Create a material function instance from the previous material function and override the parameter


  • Create a material and use the MFI from the previous step

  • Validate the project

Expected Result

The project should validate.

Observed Result

The project does not validate, with the following error message.

LogValkyrieValidation: Error: Disallowed reference to /Script/Engine.MaterialFunctionInterfaceEditorOnlyData, Referenced by:Content/Temp/mfi_test.uasset (MaterialFunctionInstance), Plugin mount point:/project_name.
UEFNValidation: Error: Disallowed reference to /Script/Engine.MaterialFunctionInterfaceEditorOnlyData, Referenced by:See below for asset list, Plugin mount point:/project_name.
UEFNValidation: Error:      /project_name/Temp/mfi_test

LogValkyrie: Error: FlowStep_RunLocalValidation(): Source content validation failed

Platform(s)

UEFN (v37.00)

To provide a bit more information:

I first discovered this issue when migrating some external UI materials that used MFIs. It’s a miracle to me that ever since the exposure of the feature, no one actually reported that it does not validate.