Lightmass not Working In Unreal 5.7 on Mac

Development Rendering
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Hi Guys!

I have an issue with Lightmass in Unreal engine 5.7, (anything above 5.4.4) on my Mac.

I have a 2021 M1 Pro MacBook Pro with 16 GB of shared ram, and it is running MacOS 26.02.

When I attempt to build lighting, even in an almost black seen, the lighting build fails after a few seconds, never going pas 0%, showing the following:

Screenshot 2025-11-15 at 12.57.47 PM
Screenshot 2025-11-15 at 12.57.47 PM760Ă—422 92.6 KB

When I then check out the errors supposedly found, all I find is:

Screenshot 2025-11-15 at 12.58.31 PM
Screenshot 2025-11-15 at 12.58.31 PM1920Ă—1200 81.9 KB

I have static lighting enabled in project settings, and the same project successfully builds in 5.4.4. Does anyone have a solution?

2 Likes
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I can only boldly guess that Epic is preparing to deprecate Lightmass.

1 Like
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Same issue for me with Unreal Engine 5.7.3 running on macOS 15.5.

Building lights worked for me with UE 5.5.4 (and only if the Mac’s Firewall is OFF), but doesn’t work in UE 5.6 nor 5.7.

How can such a basic feature be broken? :frowning:

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Hasn’t worked on Linux since 5.4 either, which came out almost two years ago.

The thing everyone should understand about Unreal is that above all else, it is an engine to make Fortnite.

That means there is no guarantee anything in the engine will continue to work unless it is something Epic needs for Fortnite… and Fortnite does not use lightmass…