It is failing trying to load a .usf file that isn't present: [2015.09.22-15.32.40:375][ 0]LogMac:Error: appError called: Assertion failed: Assertion failed: File:/Users/build/BuildFarm/build_++depot+UE4-Releases+4.9/Engine/Source/Runtime/ShaderCore/Private/ShaderCore.cpp [Line: 357] Couldn't load shader file 'LpvDirectionalOcclusion' This isn't a bug in any Mac specific code - this shader isn't found on his system either because it wasn't bundled into the build (but should have been according to P4), or his install is incomplete, or because he's running a case-sensitive file-system (which we don't support on OS X).
User reporting he is crashing when launching the Editor
"This is a 4.9.1 binary build (latest), I can't give you the exact version because it crashes on the initialisation stage at 0%. The system is a mac mini i5 running osx 10.10.5."
The user also mentioned he does not receive this crash in 4.8.3 - 2634408
Could not reproduce on the Mac we have here.
Tested in Binary 4.9.1 - 2689999
Link to Crash Reporter
Head over to the existingAnswerHub thread and let us know what's up.