Roughness not working on Non-Metal materials after reverting from Substrate to Legacy

Hi everyone,

I recently enabled the Substrate framework in my Unreal Engine 5 project to test its features. However, after deciding to revert back to the Legacy Material System (disabling “Substrate Materials” in Project Settings and restarting), I’ve encountered a critical issue with my materials.

The Issue: The Roughness input no longer seems to affect Non-Metal (Dielectric) materials. Regardless of the value or texture plugged into the Roughness slot, the surfaces appear either fully glossy or have a broken specular response.

This issue persists even after: Deleting the DerivedDataCache folder.

Has anyone else experienced this “broken” roughness state after disabling Substrate? Is there a specific console command or a hidden setting that needs to be reset to restore the standard PBR roughness behavior for non-metals?

Any help or insight would be greatly appreciated!