Unreal (5.4.4 and 5.6 Preview) Lightmass on Mac stopping at 0%

Jonathan Cooper
Tue, 27 May 2025 19:08:22 +0000
Rendering

I am unable to get Unreal to build lighting on an Apple MacBook Pro M4, with it stopping at 0% before failing, and offering no errors beyond:

LogStaticLightingSystem: Warning: Failed to build lighting!!! Lighting build failed.
DumpUnbuiltLightIteractions
Lights with unbuilt interactions: 0
Primitives with unbuilt interactions: 0
Cmd: MAP CHECK NOTIFYRESULTS
MapCheck: Map check complete: 0 Error(s), 0 Warning(s), took 0.09ms to complete.

I have followed tutorials for building lights, but no success. This was in 5.4.4 and I see the same in the 5.6 preview. I have found a couple of other posts mentioning the same issue, but none with a resolution that works (others mention lightness requiring a firewall exception but mine is off).

Is it the case that baked lighting (like GPU Lightmass) is simply untested or unavailable on Apple Silicon? I can’t find any official mention of this on Epic announcements. Has anyone else successfully built lighting on an M4 Mac?

13 posts - 9 participants