Still present in 43.00: Material Function Instance assets always fail UEFN validation (their editor-only data class is not on the allow-list)

General Issues and Bug Reporting
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Summary

Follow-up to the locked report Material Function Instance does not validate (FORT-954202, on the To Do list since 2025-08-25). That topic no longer takes replies, so this new topic carries the 43.00 status: the bug is still present. Any MaterialFunctionInstance created in UEFN fails project validation, because the instance package serializes editor-only data under /Script/Engine.MaterialFunctionInterfaceEditorOnlyData and that class is still missing from the class allow-list in 43.00, while the three sibling editor-only-data classes (for Material, MaterialFunction and MaterialInstance) are present. MaterialFunctionInstances therefore still cannot ship in published islands.

Please select what you are reporting on:

Unreal Editor for Fortnite

What Type of Bug are you experiencing?

Assets

Steps to Reproduce

  1. In any UEFN project, create a Material Function.
  2. Create a Material Function Instance with that function as its parent.
  3. Save both assets and run project validation (or attempt to publish).

Expected Result

The Material Function Instance validates like its parent, since the editor’s own factory created it and its sibling asset kinds’ editor-only-data classes are all allow-listed.

Observed Result

The instance asset is reported invalid on the /Script/Engine.MaterialFunctionInterfaceEditorOnlyData class reference, which the factory itself serialized. The parent function and a material consuming the instance both validate, but the instance cannot ship, which blocks the feature end to end.

Platform(s)

PC (Windows)

Additional Notes

What was checked for 43.00: the class allow-lists that ship with the 43.00 editor. ValkyrieSentryManifest.jsonstill list only MaterialEditorOnlyData, MaterialFunctionEditorOnlyData and MaterialInstanceEditorOnlyData of the Material*EditorOnlyData classes; /Script/Engine.MaterialFunctionInterfaceEditorOnlyData is absent from both. 43.00 newly allows /Script/Engine.MaterialInterface, but that is the abstract base class, not the missing editor-only-data class, so it does not change the result. The validation failure itself was observed in the editor in the original report; the 43.00 check is of the shipped allow-lists. Internal bug database reference, for matching any follow-up to our records: MF7QR3.