Build LIghting on Mac BROKEN

Development Rendering
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Cannot build lighting on a Mac. M3 Ultra, but I’ve had one of my colleagues also try on his M2 laptop and he gets the same result. Completely broken and I am dead in the water.

I get “Lighting Build Failed.” That’s the error. That’s all I get. I’ve even tried opening a brand new generic scene from the default Unreal library. Lighting Build Failed.

Yes, I have static lighting enabled. Yes, I have Lumen turned off.

I’ve searched the internet and tried all of these things and nothing works. Please help!

  • Fix UnrealLightmass Permissions:

    • Navigate to your Unreal Engine installation folder (e.g., /Users/Shared/Epic Games/UE_5.x/Engine/Binaries/Mac/).

    • Right-click UnrealLightmass, select Get Info, and ensure all accounts under Sharing & Permissions are set to Read & Write.

  • macOS Firewall/Security:

    • Add UnrealLightmass to the allowed applications in your Mac’s firewall settings.

    • Alternatively, temporarily disable your firewall to see if it allows the build to proceed.

  • Toggle UDP Messaging:

    • Go to Edit > Plugins, search for “UDP Messaging,” and ensure it is enabled, as it is required for network communication during lighting builds.

  • Use GPU Lightmass:

    • If Swarm Agent (CPU) fails, try switching to GPU Lightmass in the Plugins menu for better performance and compatibility on Metal/Mac.

  • Clear Cache:

    • Delete the DerivedDataCache and Saved folders in your project directory, then attempt to rebuild.

  • Ensure Xcode is Installed:

    • Make sure Xcode is installed and the license agreement has been accepted to allow proper shader compilation.